Microwave field stimulator

ABSTRACT

A system includes a controller module, which includes a storage device, a controller, a modulator, and one or more antennas. The storage device is stored with parameters defining a stimulation waveform. The controller is configured to generate, based on the stored parameters, an output signal that includes the stimulation waveform, wherein the output signal additionally includes polarity assignments for electrodes in an implantable, passive stimulation device. The modulator modulates a stimulus carrier signal with the output signal to generate a transmission signal. The one or more antennas transmit the transmission signal to the implantable, passive stimulation device such that the implantable, passive stimulation device uses energy in the transmission signal for operation, sets the polarities for the electrodes in the implantable, passive stimulation device based on the encoded polarity assignments, generates electrical pulses using the stimulation waveform, and applies the electrical pulses to excitable tissue.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/522,812, filed Aug. 12, 2011. This application is acontinuation-in-part of U.S. application Ser. No. 13/562,221, filed Jul.30, 2012, which claims benefit of U.S. Provisional Application Ser. No.61/513,397, filed Jul. 29, 2011, and is a continuation-in-part of PCTApplication PCT/US2012/023029, filed Jan. 27, 2012, which claims benefitof U.S. Provisional Application Ser. No. 61/437,561, filed Jan. 28,2011. All of the proceeding applications are hereby incorporated byreference in their entirety.

BACKGROUND

Neural modulation of neural tissue in the body by electrical stimulationhas become an important type of therapy for chronic disablingconditions, such as chronic pain, problems of movement initiation andcontrol, involuntary movements, dystonia, urinary and fecalincontinence, sexual difficulties, vascular insufficiency, heartarrhythmia and more. Electrical stimulation of the spinal column andnerve bundles leaving the spinal cord was the first approved neuralmodulation therapy and been used commercially since the 1970s. Implantedelectrodes are used to pass pulsatile electrical currents ofcontrollable frequency, pulse width and amplitudes. Two or moreelectrodes are in contact with neural elements, chiefly axons, and canselectively activate varying diameters of axons, with positivetherapeutic benefits. A variety of therapeutic intra-body electricalstimulation techniques are utilized to treat neuropathic conditions thatutilize an implanted neural stimulator in the spinal column orsurrounding areas, including the dorsal horn, dorsal root ganglia,dorsal roots, dorsal column fibers and peripheral nerve bundles leavingthe dorsal column or brain, such as vagus-, occipital-, trigeminal,hypoglossal-, sacral-, and coccygeal nerves.

SUMMARY

In one aspect, a system includes a controller module. The controllermodule includes a storage device, a controller, a modulator, and one ormore antennas. The storage device is configured to store parametersdefining a stimulation waveform. The controller is configured togenerate, based on the stored parameters, an output signal that includesthe stimulation waveform. The output signal additionally includespolarity assignments for electrodes in an implantable passive neuralstimulation device. The modulator configured to modulate a carriersignal with the output signal to generate a transmission signal. The oneor more antennas configured to transmit the transmission signal to theimplantable, passive stimulation device such that the implantable,passive stimulation device uses energy in the transmission signal foroperation, sets the polarities for the electrodes in the implantable,passive stimulation device based on the encoded polarity assignments,generates electrical pulses using the stimulation waveform, and appliesthe electrical pulses to excitable tissue.

Implementations of this and other aspects may include the followingfeatures. The stimulation waveform may include a sequence of pulses andthe stored parameters include at least one of: a pulse duration, pulseamplitude, and a pulse repetition rate. The output signal generated bythe controller may include a configuration portion that encodes thepolarity assignments and a stimulation portion that includes thestimulation waveform.

The controller module may be configured to generate the transmissionsignal such that the transmission signal has an initial power-on portionthat precedes the configuration portion and the stimulation portion, theinitial portion being sent to the implantable, passive stimulationdevice as part of the transmission signal such that the implantable,passive stimulation device stores energy from the initial power-onportion and sends a power-on event signal when the stored energy reachesa threshold amount.

The controller module may be further configured to: receive the power-onevent signal from the implantable passive stimulator; in response toreceiving the power-on event signal, generate the configuration portionthat is sent to the implantable passive stimulation device; and aftergenerating the configuration portion, generate the stimulation portion.The configuration portion may include multiple waveform edges thatencode the polarity assignments.

The controller module may further include a rechargeable power sourcemanaged by a power management protocol. The power management protocolmay include: a level in which the receiver is configured to ignoretelemetry feedback signal from the implantable passive stimulationdevice. The rechargeable power source may include one of: a lithium-ionbattery, a lithium polymer battery.

The system may further include a programmer module having a visualprogramming interface to enable a user to program the controller module.The visual programming module may be configured to authenticate the userand thereafter provide access control to the user.

In some implementations of the system, the one or more antennas may befurther configured to receive telemetry feedback signals from theimplantable passive device in response to the transmission signal, andthe controller may be further configured to modify the output signal byusing a closed-loop feedback control based on the received telemetryfeedback signal.

In one implementation, the controller may be further programmed to applythe closed-loop feedback control by: ascertaining a distortion to theelectrical pulses as applied by the electrodes of the implantable,passive stimulation device, the distortion caused by at least one of atransmission characteristic of the antenna, a characteristic of theimplantable passive stimulation device, or an impedance characteristicof the tissue; and adjusting the stimulation waveform embedded in thetransmission signal to compensate the distortion such that theelectrical pulses as applied are substantially undistorted despite thetransmission characteristic of the antenna, the characteristic of theimplantable passive stimulation device, or the impedance characteristicof the tissue. The distortion may be characterized as a frequencyresponse corresponding to at least one of the transmissioncharacteristic of the antenna, the characteristic of the implantablepassive stimulation device, and the impedance characteristic of thetissue. The adjustment may be by filtering the transmission signalaccording to an inverse of the frequency response.

In another implementation, the controller may be further programmed toapply the closed-loop feedback control by: monitoring a stimulus powerbeing directed to the tissue through the electrodes based on informationcontained in the telemetry feedback signal; and adjusting a parameterassociated with the stimulation waveform embedded in the transmissionsignal such that the stimulus power remains substantially constant.Changes in the stimulus power are induced by patient body movement. Theparameter may include an amplitude level associated with the stimulationwaveform, and the amplitude level may be adjusted based on a lookuptable showing a relationship between the amplitude level and acorresponding power applied to the tissue through the electrodes. Theadjustments may include modifying the carrier frequency within a rangeof up to 10 megahertz.

The storage device may include non-volatile memory including at leastone of: an EEPROM, a flash memory.

The controller module is placed within a 3-feet radius of theimplantable, passive stimulation device. The controller module may beplaced as a sub-cutaneous implantation. In another aspect, a systemincludes a controller module. The controller module includes a storagedevice, a controller, a modulator, and one or more antennas. The storagedevice is configured to store parameters defining a stimulation waveformand polarity assignments for electrodes in an implantable, passivestimulation device that includes a power-on reset circuit, controllogic, stimulation circuitry, and stimulation electrodes. The controlleris configured to generate, based on the stored parameters and polarityassignments, an output signal that includes an initial power-on portionfollowed by a configuration portion that encodes the polarityassignments followed by a stimulation portion that includes thestimulation waveform. The modulator is configured to modulate a carriersignal with the output signal to generate a transmission signal. The oneor more antennas are configured to transmit the transmission signal tothe implantable passive stimulation device such that the power-on resetcircuit uses energy in the power-on portion to generate a power-on resetsignal that resets the control logic, the control logic reads thepolarity assignment information encoded in the configuration portion andsets the polarities for the electrodes, and the stimulation circuitrygenerates electrical pulses using the stimulation waveform and appliesthe electrical pulses to excitable tissue.

Implementations of this and other aspects may include the followingfeatures. The controller module may be configured to read a telemetryfeedback signal from the implantable passive stimulation device, thetelemetry signal generated by: sensing a first electrical parameter anda second electrical parameter concurrently; and comparing the firstelectrical parameter and the second electrical parameter to generate ananalog carrier frequency signal with a stimulus carrier frequency thatis proportional to a difference between the first electrical parameterand the second electrical parameter.

The first electrical parameter may be a voltage over a referenceresistor placed in serial connection with the electrode, and the secondelectrical parameter may be a voltage over the electrode. The stimuluscarrier frequency may be proportional to a difference between a voltageover the reference resistor and a voltage over the electrode.

The first electrical parameter may be a voltage over a referenceresistor placed in serial connection with the electrode, and the secondelectrical parameter may be a voltage over a calibration resister placedin parallel connection with the electrode. The stimulus carrierfrequency may be proportional to a difference between a voltage over thereference resistor and the voltage over the calibration resistor.

The first electrical parameter may correspond to a fixed voltage and thesecond electrical parameter may be a voltage over one of: a calibrationresistor, a reference resistor, an electrode.

The power-on signal may cause a handshake signal to be transmitted fromimplantable, passive stimulator to the controller module, the handshakesignal confirms to the controller module that the implantable, passivestimulation device is ready to receive polarity setting information.

The handshake signal may be received from the implantable, passivestimulator when the polarities for the electrodes are set according tothe polarity assignment information encoded in the configurationportion, the handshake signal confirms to the controller module that theimplantable, passive stimulator is ready to receive the stimulationportion of the transmission signal.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts a high-level diagram of an example of a wireless neuralstimulation system.

FIGS. 2A and 2B depict a detailed diagram of an example of the wirelessneural stimulation system.

FIG. 3 is a flowchart showing an example of the operation of thewireless neural stimulator system.

FIG. 4 depicts a flow chart showing an example of the operation of thesystem when the current level at the electrodes is above the thresholdlimit.

FIG. 5 is a diagram showing examples of signals that may be used todetect an impedance mismatch.

FIG. 6 is a diagram showing examples of signals that may be employedduring operation of the wireless neural stimulator system.

FIG. 7 is a flow chart showing a process for the user to control theimplantable wireless neural stimulator through an external programmer inan open loop feedback system.

FIGS. 8A and 8B show another example flow chart of a process for theuser to control the wireless stimulator with limitations on the lowerand upper limits of current amplitude.

FIG. 9 is yet another example flow chart of a process for the user tocontrol the wireless neural stimulator through preprogrammed parametersettings.

FIG. 10 is still another example flow chart of a process for a lowbattery state for the RF pulse generator module.

FIG. 11 is yet another example flow chart of a process for aManufacturer's Representative to program the implanted wireless neuralstimulator.

FIG. 12 is a circuit diagram showing an example of a wireless neuralstimulator.

FIG. 13 is a circuit diagram of another example of a wireless neuralstimulator.

FIG. 14 is a block diagram showing an example of control and feedbackfunctions of a wireless implantable neural stimulator.

FIG. 15 is a schematic showing an example of a wireless implantableneural stimulator with components to implement control and feedbackfunctions.

FIG. 16 shows an example of a pulse waveform seen at the powermanagement circuitry of a wireless implantable neural stimulator.

FIG. 17 is a schematic of an example of a polarity routing switchnetwork.

FIGS. 18A and 18B, respectively show an example of a waveform generatedby a rectifying circuit of a wireless neural stimulator and thecorresponding spectrum.

FIG. 19 is a flow chart illustrating an example of the operations ofcontrol and feedback functions of a wireless implantable neuralstimulator.

FIG. 20A is a diagram of an example microwave field stimulator (MFS)operating along with an implantable stimulation device.

FIG. 20B is a diagram of another example microwave field stimulator(MFS) operating along with an implantable stimulation device.

FIG. 21 is a detailed diagram of an example microwave field stimulator.

FIG. 22 is a flowchart showing an example process in which the MFStransmits polarity setting information to the implanted lead module.

FIG. 23 is another flow chart showing an example process in which theMFS receives and processes the telemetry feedback signal to makeadjustments to subsequent transmissions.

FIG. 24 is a schematic of an example implementation of power, signal andcontrol flow on the implanted lead module.

FIG. 25A shows an example RF carrier wave and example envelope waveformssuitable for use as stimulation waveforms.

FIG. 25B shows an example pre-distorted stimulation waveform to offsetdistortions caused by the MFS and the implanted lead module as well asthe impedance characteristic of the tissue being stimulated.

FIG. 26 is a timing diagram showing example waveforms during the initialportion and the subsequent configuration portion of a transmissionsignal received at the implantable, passive stimulation device.

FIG. 27 is a timing diagram showing example waveforms during the finalstimulation portion of the transmission signal received at theimplantable, passive stimulation device.

FIG. 28 is a block diagram illustrating an example in which a userprograms the stimulation waveform to be embedded in the signal sequencefor transmission to the implanted lead module.

FIG. 29A shows an example user interface for the user to program thestimulation waveform.

FIG. 29B shows another example user interface for the user to programthe stimulation waveform.

DETAILED DESCRIPTION

In various implementations, a neural stimulation system may be used tosend electrical stimulation to targeted nerve tissue by using remoteradio frequency (RF) energy with neither cables nor inductive couplingto power the passive implanted stimulator. The targeted nerve tissuesmay be, for example, in the spinal column including the spinothalamictracts, dorsal horn, dorsal root ganglia, dorsal roots, dorsal columnfibers, and peripheral nerves bundles leaving the dorsal column orbrainstem, as well as any cranial nerves, abdominal, thoracic, ortrigeminal ganglia nerves, nerve bundles of the cerebral cortex, deepbrain and any sensory or motor nerves.

For instance, in some implementations, the neural stimulation system mayinclude a controller module, such as an RF pulse generator module, and apassive implanted neural stimulator that contains one or more dipoleantennas, one or more circuits, and one or more electrodes in contactwith or in proximity to targeted neural tissue to facilitatestimulation. The RF pulse generator module may include an antenna andmay be configured to transfer energy from the module antenna to theimplanted antennas. The one or more circuits of the implanted neuralstimulator may be configured to generate electrical pulses suitable forneural stimulation using the transferred energy and to supply theelectrical pulses to the electrodes so that the pulses are applied tothe neural tissue. For instance, the one or more circuits may includewave conditioning circuitry that rectifies the received RF signal (forexample, using a diode rectifier), transforms the RF energy to a lowfrequency signal suitable for the stimulation of neural tissue, andpresents the resulting waveform to an electrode array. The one or morecircuits of the implanted neural stimulator may also include circuitryfor communicating information back to the RF pulse generator module tofacilitate a feedback control mechanism for stimulation parametercontrol. For example, the implanted neural stimulator may send to the RFpulse generator module a stimulus feedback signal that is indicative ofparameters of the electrical pulses, and the RF pulse generator modulemay employ the stimulus feedback signal to adjust parameters of thesignal sent to the neural stimulator.

FIG. 1 depicts a high-level diagram of an example of a neuralstimulation system. The neural stimulation system may include four majorcomponents, namely, a programmer module 102, a RF pulse generator module106, a transmit (TX) antenna 110 (for example, a patch antenna, slotantenna, or a dipole antenna), and an implanted wireless neuralstimulator 114. The programmer module 102 may be a computer device, suchas a smart phone, running a software application that supports awireless connection 114, such as Bluetooth®. The application can enablethe user to view the system status and diagnostics, change variousparameters, increase/decrease the desired stimulus amplitude of theelectrode pulses, and adjust feedback sensitivity of the RF pulsegenerator module 106, among other functions.

The RF pulse generator module 106 may include communication electronicsthat support the wireless connection 104, the stimulation circuitry, andthe battery to power the generator electronics. In some implementations,the RF pulse generator module 106 includes the TX antenna embedded intoits packaging form factor while, in other implementations, the TXantenna is connected to the RF pulse generator module 106 through awired connection 108 or a wireless connection (not shown). The TXantenna 110 may be coupled directly to tissue to create an electricfield that powers the implanted neural stimulator module 114. The TXantenna 110 communicates with the implanted neural stimulator module 114through an RF interface. For instance, the TX antenna 110 radiates an RFtransmission signal that is modulated and encoded by the RF pulsegenerator module 110. The implanted wireless neural stimulator module114 contains one or more antennas, such as dipole antenna(s), to receiveand transmit through RF interface 112. In particular, the couplingmechanism between antenna 110 and the one or more antennas on theimplanted neural stimulation module 114 is electrical radiative couplingand not inductive coupling. In other words, the coupling is through anelectric field rather than a magnetic field.

Through this electrical radiative coupling, the TX antenna 110 canprovide an input signal to the implanted neural stimulation module 114.This input signal contains energy and may contain information encodingstimulus waveforms to be applied at the electrodes of the implantedneural stimulator module 114. In some implementations, the power levelof this input signal directly determines an applied amplitude (forexample, power, current, or voltage) of the one or more electricalpulses created using the electrical energy contained in the inputsignal. Within the implanted wireless neural stimulator 114 arecomponents for demodulating the RF transmission signal, and electrodesto deliver the stimulation to surrounding neuronal tissue.

The RF pulse generator module 106 can be implanted subcutaneously, or itcan be worn external to the body. When external to the body, the RFgenerator module 106 can be incorporated into a belt or harness designto allow for electric radiative coupling through the skin and underlyingtissue to transfer power and/or control parameters to the implantedneural stimulator module 114, which can be a passive stimulator. Ineither event, receiver circuit(s) internal to the neural stimulatormodule 114 can capture the energy radiated by the TX antenna 110 andconvert this energy to an electrical waveform. The receiver circuit(s)may further modify the waveform to create an electrical pulse suitablefor the stimulation of neural tissue, and this pulse may be delivered tothe tissue via electrode pads.

In some implementations, the RF pulse generator module 106 can remotelycontrol the stimulus parameters (that is, the parameters of theelectrical pulses applied to the neural tissue) and monitor feedbackfrom the wireless neural stimulator module 114 based on RF signalsreceived from the implanted wireless neural stimulator module 114. Afeedback detection algorithm implemented by the RF pulse generatormodule 106 can monitor data sent wirelessly from the implanted wirelessneural stimulator module 114, including information about the energythat the implanted wireless neural stimulator module 114 is receivingfrom the RF pulse generator and information about the stimulus waveformbeing delivered to the electrode pads. In order to provide an effectivetherapy for a given medical condition, the system can be tuned toprovide the optimal amount of excitation or inhibition to the nervefibers by electrical stimulation. A closed loop feedback control methodcan be used in which the output signals from the implanted wirelessneural stimulator module 114 are monitored and used to determine theappropriate level of neural stimulation current for maintainingeffective neuronal activation, or, in some cases, the patient canmanually adjust the output signals in an open loop control method.

FIGS. 2A and 2B depicts a detailed diagram of an example of the neuralstimulation system. As depicted, the programming module 102 may compriseuser input system 202 and communication subsystem 208. The user inputsystem 221 may allow various parameter settings to be adjusted (in somecases, in an open loop fashion) by the user in the form of instructionsets. The communication subsystem 208 may transmit these instructionsets (and other information) via the wireless connection 104, such asBluetooth or Wi-Fi, to the RF pulse generator module 106, as well asreceive data from module 106.

For instance, the programmer module 102, which can be utilized formultiple users, such as a patient's control unit or clinician'sprogrammer unit, can be used to send stimulation parameters to the RFpulse generator module 106. The stimulation parameters that can becontrolled may include pulse amplitude, pulse frequency, and pulse widthin the ranges shown in Table 1. In this context the term pulse refers tothe phase of the waveform that directly produces stimulation of thetissue; the parameters of the charge-balancing phase (described below)can similarly be controlled. The patient and/or the clinician can alsooptionally control overall duration and pattern of treatment.

STIMULATION PARAMETER TABLE 1 Pulse Amplitude: 0 to 20 mA PulseFrequency: 0 to 2000 Hz Pulse Width: 0 to 2 ms

The implantable neural stimulator module 114 or RF pulse generatormodule 114 may be initially programmed to meet the specific parametersettings for each individual patient during the initial implantationprocedure. Because medical conditions or the body itself can change overtime, the ability to re-adjust the parameter settings may be beneficialto ensure ongoing efficacy of the neural modulation therapy.

The programmer module 102 may be functionally a smart device andassociated application. The smart device hardware may include a CPU 206and be used as a vehicle to handle touchscreen input on a graphical userinterface (GUI) 204, for processing and storing data.

The RF pulse generator module 106 may be connected via wired connection108 to an external TX antenna 110. Alternatively, both the antenna andthe RF pulse generator are located subcutaneously (not shown).

The signals sent by RF pulse generator module 106 to the implantedstimulator 114 may include both power and parameter-setting attributesin regards to stimulus waveform, amplitude, pulse width, and frequency.The RF pulse generator module 106 can also function as a wirelessreceiving unit that receives feedback signals from the implantedstimulator module 114. To that end, the RF pulse generator module 106may contain microelectronics or other circuitry to handle the generationof the signals transmitted to the stimulator module 114 as well ashandle feedback signals, such as those from the stimulator module 114.For example, the RF pulse generator module 106 may comprise controllersubsystem 214, high-frequency oscillator 218, RF amplifier 216, a RFswitch, and a feedback subsystem 212.

The controller subsystem 214 may include a CPU 230 to handle dataprocessing, a memory subsystem 228 such as a local memory, communicationsubsystem 234 to communicate with programmer module 102 (includingreceiving stimulation parameters from programmer module), pulsegenerator circuitry 236, and digital/analog (D/A) converters 232.

The controller subsystem 214 may be used by the patient and/or theclinician to control the stimulation parameter settings (for example, bycontrolling the parameters of the signal sent from RF pulse generatormodule 106 to neural stimulator module 114). These parameter settingscan affect, for example, the power, current level, or shape of the oneor more electrical pulses. The programming of the stimulation parameterscan be performed using the programming module 102, as described above,to set the repetition rate, pulse width, amplitude, and waveform thatwill be transmitted by RF energy to the receive (RX) antenna 238,typically a dipole antenna (although other types may be used), in thewireless implanted neural stimulator module 214. The clinician may havethe option of locking and/or hiding certain settings within theprogrammer interface, thus limiting the patient's ability to view oradjust certain parameters because adjustment of certain parameters mayrequire detailed medical knowledge of neurophysiology, neuroanatomy,protocols for neural modulation, and safety limits of electricalstimulation.

The controller subsystem 214 may store received parameter settings inthe local memory subsystem 228, until the parameter settings aremodified by new input data received from the programming module 102. TheCPU 206 may use the parameters stored in the local memory to control thepulse generator circuitry 236 to generate a stimulus waveform that ismodulated by a high frequency oscillator 218 in the range from 300 MHzto 8 GHz. The resulting RF signal may then be amplified by RF amplifier226 and then sent through an RF switch 223 to the TX antenna 110 toreach through depths of tissue to the RX antenna 238.

In some implementations, the RF signal sent by TX antenna 110 may simplybe a power transmission signal used by stimulator module 114 to generateelectric pulses. In other implementations, a telemetry signal may alsobe transmitted to the stimulator module 114 to send instructions aboutthe various operations of the stimulator module 114. The telemetrysignal may be sent by the modulation of the carrier signal (through theskin if external, or through other body tissues if the pulse generatormodule 106 is implanted subcutaneously). The telemetry signal is used tomodulate the carrier signal (a high frequency signal) that is coupledonto the implanted antenna(s) 238 and does not interfere with the inputreceived on the same lead to power the implant. In one embodiment thetelemetry signal and powering signal are combined into one signal, wherethe RF telemetry signal is used to modulate the RF powering signal, andthus the implanted stimulator is powered directly by the receivedtelemetry signal; separate subsystems in the stimulator harness thepower contained in the signal and interpret the data content of thesignal.

The RF switch 223 may be a multipurpose device such as a dualdirectional coupler, which passes the relatively high amplitude,extremely short duration RF pulse to the TX antenna 110 with minimalinsertion loss while simultaneously providing two low-level outputs tofeedback subsystem 212; one output delivers a forward power signal tothe feedback subsystem 212, where the forward power signal is anattenuated version of the RF pulse sent to the TX antenna 110, and theother output delivers a reverse power signal to a different port of thefeedback subsystem 212, where reverse power is an attenuated version ofthe reflected RF energy from the TX Antenna 110.

During the on-cycle time (when an RF signal is being transmitted tostimulator 114), the RF switch 223 is set to send the forward powersignal to feedback subsystem. During the off-cycle time (when an RFsignal is not being transmitted to the stimulator module 114), the RFswitch 223 can change to a receiving mode in which the reflected RFenergy and/or RF signals from the stimulator module 114 are received tobe analyzed in the feedback subsystem 212.

The feedback subsystem 212 of the RF pulse generator module 106 mayinclude reception circuitry to receive and extract telemetry or otherfeedback signals from the stimulator 114 and/or reflected RF energy fromthe signal sent by TX antenna 110. The feedback subsystem may include anamplifier 226, a filter 224, a demodulator 222, and an A/D converter220.

The feedback subsystem 212 receives the forward power signal andconverts this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. In this way thecharacteristics of the generated RF pulse can be compared to a referencesignal within the controller subsystem 214. If a disparity (error)exists in any parameter, the controller subsystem 214 can adjust theoutput to the RF pulse generator 106. The nature of the adjustment canbe, for example, proportional to the computed error. The controllersubsystem 214 can incorporate additional inputs and limits on itsadjustment scheme such as the signal amplitude of the reverse power andany predetermined maximum or minimum values for various pulseparameters.

The reverse power signal can be used to detect fault conditions in theRF-power delivery system. In an ideal condition, when TX antenna 110 hasperfectly matched impedance to the tissue that it contacts, theelectromagnetic waves generated from the RF pulse generator 106 passunimpeded from the TX antenna 110 into the body tissue. However, inreal-world applications a large degree of variability may exist in thebody types of users, types of clothing worn, and positioning of theantenna 110 relative to the body surface. Since the impedance of theantenna 110 depends on the relative permittivity of the underlyingtissue and any intervening materials, and also depends on the overallseparation distance of the antenna from the skin, in any givenapplication there can be an impedance mismatch at the interface of theTX antenna 110 with the body surface. When such a mismatch occurs, theelectromagnetic waves sent from the RF pulse generator 106 are partiallyreflected at this interface, and this reflected energy propagatesbackward through the antenna feed.

The dual directional coupler RF switch 223 may prevent the reflected RFenergy propagating back into the amplifier 226, and may attenuate thisreflected RF signal and send the attenuated signal as the reverse powersignal to the feedback subsystem 212. The feedback subsystem 212 canconvert this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. The controller subsystem 214can then calculate the ratio of the amplitude of the reverse powersignal to the amplitude of the forward power signal. The ratio of theamplitude of reverse power signal to the amplitude level of forwardpower may indicate severity of the impedance mismatch.

In order to sense impedance mismatch conditions, the controllersubsystem 214 can measure the reflected-power ratio in real time, andaccording to preset thresholds for this measurement, the controllersubsystem 214 can modify the level of RF power generated by the RF pulsegenerator 106. For example, for a moderate degree of reflected power thecourse of action can be for the controller subsystem 214 to increase theamplitude of RF power sent to the TX antenna 110, as would be needed tocompensate for slightly non-optimum but acceptable TX antenna couplingto the body. For higher ratios of reflected power, the course of actioncan be to prevent operation of the RF pulse generator 106 and set afault code to indicate that the TX antenna 110 has little or no couplingwith the body. This type of reflected-power fault condition can also begenerated by a poor or broken connection to the TX antenna. In eithercase, it may be desirable to stop RF transmission when thereflected-power ratio is above a defined threshold, because internallyreflected power can lead to unwanted heating of internal components, andthis fault condition means the system cannot deliver sufficient power tothe implanted wireless neural stimulator and thus cannot deliver therapyto the user.

The controller 242 of the stimulator 114 may transmit informationalsignals, such as a telemetry signal, through the antenna 238 tocommunicate with the RF pulse generator module 106 during its receivecycle. For example, the telemetry signal from the stimulator 114 may becoupled to the modulated signal on the dipole antenna(s) 238, during theon and off state of the transistor circuit to enable or disable awaveform that produces the corresponding RF bursts necessary to transmitto the external (or remotely implanted) pulse generator module 106. Theantenna(s) 238 may be connected to electrodes 254 in contact with tissueto provide a return path for the transmitted signal. An A/D (not shown)converter can be used to transfer stored data to a serialized patternthat can be transmitted on the pulse modulated signal from the internalantenna(s) 238 of the neural stimulator.

A telemetry signal from the implanted wireless neural stimulator module114 may include stimulus parameters such as the power or the amplitudeof the current that is delivered to the tissue from the electrodes. Thefeedback signal can be transmitted to the RF pulse generator module 116to indicate the strength of the stimulus at the nerve bundle by means ofcoupling the signal to the implanted RX antenna 238, which radiates thetelemetry signal to the external (or remotely implanted) RF pulsegenerator module 106. The feedback signal can include either or both ananalog and digital telemetry pulse modulated carrier signal. Data suchas stimulation pulse parameters and measured characteristics ofstimulator performance can be stored in an internal memory device withinthe implanted neural stimulator 114, and sent on the telemetry signal.The frequency of the carrier signal may be in the range of at 300 MHz to8 GHz.

In the feedback subsystem 212, the telemetry signal can be downmodulated using demodulator 222 and digitized by being processed throughan analog to digital (A/D) converter 220. The digital telemetry signalmay then be routed to a CPU 230 with embedded code, with the option toreprogram, to translate the signal into a corresponding currentmeasurement in the tissue based on the amplitude of the received signal.The CPU 230 of the controller subsystem 214 can compare the reportedstimulus parameters to those held in local memory 228 to verify thestimulator(s) 114 delivered the specified stimuli to tissue. Forexample, if the stimulator reports a lower current than was specified,the power level from the RF pulse generator module 106 can be increasedso that the implanted neural stimulator 114 will have more availablepower for stimulation. The implanted neural stimulator 114 can generatetelemetry data in real time, for example, at a rate of 8 kbits persecond. All feedback data received from the implanted lead module 114can be logged against time and sampled to be stored for retrieval to aremote monitoring system accessible by the health care professional fortrending and statistical correlations.

The sequence of remotely programmable RF signals received by theinternal antenna(s) 238 may be conditioned into waveforms that arecontrolled within the implantable stimulator 114 by the controlsubsystem 242 and routed to the appropriate electrodes 254 that areplaced in proximity to the tissue to be stimulated. For instance, the RFsignal transmitted from the RF pulse generator module 106 may bereceived by RX antenna 238 and processed by circuitry, such as waveformconditioning circuitry 240, within the implanted wireless neuralstimulator module 114 to be converted into electrical pulses applied tothe electrodes 254 through electrode interface 252. In someimplementations, the implanted stimulator 114 contains between two tosixteen electrodes 254.

The waveform conditioning circuitry 240 may include a rectifier 244,which rectifies the signal received by the RX antenna 238. The rectifiedsignal may be fed to the controller 242 for receiving encodedinstructions from the RF pulse generator module 106. The rectifiersignal may also be fed to a charge balance component 246 that isconfigured to create one or more electrical pulses based such that theone or more electrical pulses result in a substantially zero net chargeat the one or more electrodes (that is, the pulses are charge balanced).The charge-balanced pulses are passed through the current limiter 248 tothe electrode interface 252, which applies the pulses to the electrodes254 as appropriate.

The current limiter 248 insures the current level of the pulses appliedto the electrodes 254 is not above a threshold current level. In someimplementations, an amplitude (for example, current level, voltagelevel, or power level) of the received RF pulse directly determines theamplitude of the stimulus. In this case, it may be particularlybeneficial to include current limiter 248 to prevent excessive currentor charge being delivered through the electrodes, although currentlimiter 248 may be used in other implementations where this is not thecase. Generally, for a given electrode having several square millimeterssurface area, it is the charge per phase that should be limited forsafety (where the charge delivered by a stimulus phase is the integralof the current). But, in some cases, the limit can instead be placed onthe current, where the maximum current multiplied by the maximumpossible pulse duration is less than or equal to the maximum safecharge. More generally, the limiter 248 acts as a charge limiter thatlimits a characteristic (for example, current or duration) of theelectrical pulses so that the charge per phase remains below a thresholdlevel (typically, a safe-charge limit).

In the event the implanted wireless neural stimulator 114 receives a“strong” pulse of RF power sufficient to generate a stimulus that wouldexceed the predetermined safe-charge limit, the current limiter 248 canautomatically limit or “clip” the stimulus phase to maintain the totalcharge of the phase within the safety limit. The current limiter 248 maybe a passive current limiting component that cuts the signal to theelectrodes 254 once the safe current limit (the threshold current level)is reached. Alternatively, or additionally, the current limiter 248 maycommunicate with the electrode interface 252 to turn off all electrodes254 to prevent tissue damaging current levels.

A clipping event may trigger a current limiter feedback control mode.The action of clipping may cause the controller to send a thresholdpower data signal to the pulse generator 106. The feedback subsystem 212detects the threshold power signal and demodulates the signal into datathat is communicated to the controller subsystem 214. The controllersubsystem 214 algorithms may act on this current-limiting condition byspecifically reducing the RF power generated by the RF pulse generator,or cutting the power completely. In this way, the pulse generator 106can reduce the RF power delivered to the body if the implanted wirelessneural stimulator 114 reports it is receiving excess RF power.

The controller 250 of the stimulator 205 may communicate with theelectrode interface 252 to control various aspects of the electrodesetup and pulses applied to the electrodes 254. The electrode interface252 may act as a multiplex and control the polarity and switching ofeach of the electrodes 254. For instance, in some implementations, thewireless stimulator 106 has multiple electrodes 254 in contact withtissue, and for a given stimulus the RF pulse generator module 106 canarbitrarily assign one or more electrodes to 1) act as a stimulatingelectrode, 2) act as a return electrode, or 3) be inactive bycommunication of assignment sent wirelessly with the parameterinstructions, which the controller 250 uses to set electrode interface252 as appropriate. It may be physiologically advantageous to assign,for example, one or two electrodes as stimulating electrodes and toassign all remaining electrodes as return electrodes.

Also, in some implementations, for a given stimulus pulse, thecontroller 250 may control the electrode interface 252 to divide thecurrent arbitrarily (or according to instructions from pulse generatormodule 106) among the designated stimulating electrodes. This controlover electrode assignment and current control can be advantageousbecause in practice the electrodes 254 may be spatially distributedalong various neural structures, and through strategic selection of thestimulating electrode location and the proportion of current specifiedfor each location, the aggregate current distribution in tissue can bemodified to selectively activate specific neural targets. This strategyof current steering can improve the therapeutic effect for the patient.

In another implementation, the time course of stimuli may be arbitrarilymanipulated. A given stimulus waveform may be initiated at a timeT_start and terminated at a time T_final, and this time course may besynchronized across all stimulating and return electrodes; further, thefrequency of repetition of this stimulus cycle may be synchronous forall the electrodes. However, controller 250, on its own or in responseto instructions from pulse generator 106, can control electrodeinterface 252 to designate one or more subsets of electrodes to deliverstimulus waveforms with non-synchronous start and stop times, and thefrequency of repetition of each stimulus cycle can be arbitrarily andindependently specified.

For example, a stimulator having eight electrodes may be configured tohave a subset of five electrodes, called set A, and a subset of threeelectrodes, called set B. Set A might be configured to use two of itselectrodes as stimulating electrodes, with the remainder being returnelectrodes. Set B might be configured to have just one stimulatingelectrode. The controller 250 could then specify that set A deliver astimulus phase with 3 mA current for a duration of 200 us followed by a400 us charge-balancing phase. This stimulus cycle could be specified torepeat at a rate of 60 cycles per second. Then, for set B, thecontroller 250 could specify a stimulus phase with 1 mA current forduration of 500 us followed by a 800 us charge-balancing phase. Therepetition rate for the set-B stimulus cycle can be set independently ofset A, say for example it could be specified at 25 cycles per second.Or, if the controller 250 was configured to match the repetition ratefor set B to that of set A, for such a case the controller 250 canspecify the relative start times of the stimulus cycles to be coincidentin time or to be arbitrarily offset from one another by some delayinterval.

In some implementations, the controller 250 can arbitrarily shape thestimulus waveform amplitude, and may do so in response to instructionsfrom pulse generator 106. The stimulus phase may be delivered by aconstant-current source or a constant-voltage source, and this type ofcontrol may generate characteristic waveforms that are static, e.g. aconstant-current source generates a characteristic rectangular pulse inwhich the current waveform has a very steep rise, a constant amplitudefor the duration of the stimulus, and then a very steep return tobaseline. Alternatively, or additionally, the controller 250 canincrease or decrease the level of current at any time during thestimulus phase and/or during the charge-balancing phase. Thus, in someimplementations, the controller 250 can deliver arbitrarily shapedstimulus waveforms such as a triangular pulse, sinusoidal pulse, orGaussian pulse for example. Similarly, the charge-balancing phase can bearbitrarily amplitude-shaped, and similarly a leading anodic pulse(prior to the stimulus phase) may also be amplitude-shaped.

As described above, the stimulator 114 may include a charge-balancingcomponent 246. Generally, for constant current stimulation pulses,pulses should be charge balanced by having the amount of cathodiccurrent should equal the amount of anodic current, which is typicallycalled biphasic stimulation. Charge density is the amount of currenttimes the duration it is applied, and is typically expressed in theunits uC/cm². In order to avoid the irreversible electrochemicalreactions such as pH change, electrode dissolution as well as tissuedestruction, no net charge should appear at the electrode-electrolyteinterface, and it is generally acceptable to have a charge density lessthan 30 uC/cm². Biphasic stimulating current pulses ensure that no netcharge appears at the electrode after each stimulation cycle and theelectrochemical processes are balanced to prevent net dc currents.Neural stimulator 114 may be designed to ensure that the resultingstimulus waveform has a net zero charge. Charge balanced stimuli arethought to have minimal damaging effects on tissue by reducing oreliminating electrochemical reaction products created at theelectrode-tissue interface.

A stimulus pulse may have a negative-voltage or current, called thecathodic phase of the waveform. Stimulating electrodes may have bothcathodic and anodic phases at different times during the stimulus cycle.An electrode that delivers a negative current with sufficient amplitudeto stimulate adjacent neural tissue is called a “stimulating electrode.”During the stimulus phase the stimulating electrode acts as a currentsink. One or more additional electrodes act as a current source andthese electrodes are called “return electrodes.” Return electrodes areplaced elsewhere in the tissue at some distance from the stimulatingelectrodes. When a typical negative stimulus phase is delivered totissue at the stimulating electrode, the return electrode has a positivestimulus phase. During the subsequent charge-balancing phase, thepolarities of each electrode are reversed.

In some implementations, the charge balance component 246 uses ablocking capacitor(s) placed electrically in series with the stimulatingelectrodes and body tissue, between the point of stimulus generationwithin the stimulator circuitry and the point of stimulus delivery totissue. In this manner, a resistor-capacitor (RC) network may be formed.In a multi-electrode stimulator, one charge-balance capacitor(s) may beused for each electrode or a centralized capacitor(s) may be used withinthe stimulator circuitry prior to the point of electrode selection. TheRC network can block direct current (DC), however it can also preventlow-frequency alternating current (AC) from passing to the tissue. Thefrequency below which the series RC network essentially blocks signalsis commonly referred to as the cutoff frequency, and in one embodimentthe design of the stimulator system may ensure the cutoff frequency isnot above the fundamental frequency of the stimulus waveform. In thisembodiment, the wireless stimulator may have a charge-balance capacitorwith a value chosen according to the measured series resistance of theelectrodes and the tissue environment in which the stimulator isimplanted. By selecting a specific capacitance value the cutofffrequency of the RC network in this embodiment is at or below thefundamental frequency of the stimulus pulse.

In other implementations, the cutoff frequency may be chosen to be at orabove the fundamental frequency of the stimulus, and in this scenariothe stimulus waveform created prior to the charge-balance capacitor,called the drive waveform, may be designed to be non-stationary, wherethe envelope of the drive waveform is varied during the duration of thedrive pulse. For example, in one embodiment, the initial amplitude ofthe drive waveform is set at an initial amplitude Vi, and the amplitudeis increased during the duration of the pulse until it reaches a finalvalue k*Vi. By changing the amplitude of the drive waveform over time,the shape of the stimulus waveform passed through the charge-balancecapacitor is also modified. The shape of the stimulus waveform may bemodified in this fashion to create a physiologically advantageousstimulus.

In some implementations, the wireless neural stimulator module 114 maycreate a drive-waveform envelope that follows the envelope of the RFpulse received by the receiving dipole antenna(s) 238. In this case, theRF pulse generator module 106 can directly control the envelope of thedrive waveform within the wireless neural stimulator 114, and thus noenergy storage may be required inside the stimulator itself. In thisimplementation, the stimulator circuitry may modify the envelope of thedrive waveform or may pass it directly to the charge-balance capacitorand/or electrode-selection stage.

In some implementations, the implanted neural stimulator 114 may delivera single-phase drive waveform to the charge balance capacitor or it maydeliver multiphase drive waveforms. In the case of a single-phase drivewaveform, for example, a negative-going rectangular pulse, this pulsecomprises the physiological stimulus phase, and the charge-balancecapacitor is polarized (charged) during this phase. After the drivepulse is completed, the charge balancing function is performed solely bythe passive discharge of the charge-balance capacitor, where isdissipates its charge through the tissue in an opposite polarityrelative to the preceding stimulus. In one implementation, a resistorwithin the stimulator facilitates the discharge of the charge-balancecapacitor. In some implementations, using a passive discharge phase, thecapacitor may allow virtually complete discharge prior to the onset ofthe subsequent stimulus pulse.

In the case of multiphase drive waveforms the wireless stimulator mayperform internal switching to pass negative-going or positive-goingpulses (phases) to the charge-balance capacitor. These pulses may bedelivered in any sequence and with varying amplitudes and waveformshapes to achieve a desired physiological effect. For example, thestimulus phase may be followed by an actively driven charge-balancingphase, and/or the stimulus phase may be preceded by an opposite phase.Preceding the stimulus with an opposite-polarity phase, for example, canhave the advantage of reducing the amplitude of the stimulus phaserequired to excite tissue.

In some implementations, the amplitude and timing of stimulus andcharge-balancing phases is controlled by the amplitude and timing of RFpulses from the RF pulse generator module 106, and in others thiscontrol may be administered internally by circuitry onboard the wirelessstimulator 114, such as controller 250. In the case of onboard control,the amplitude and timing may be specified or modified by data commandsdelivered from the pulse generator module 106.

FIG. 3 is a flowchart showing an example of an operation of the neuralstimulator system. In block 302, the wireless neural stimulator 114 isimplanted in proximity to nerve bundles and is coupled to the electricfield produced by the TX antenna 110. That is, the pulse generatormodule 106 and the TX antenna 110 are positioned in such a way (forexample, in proximity to the patient) that the TX antenna 110 iselectrically radiatively coupled with the implanted RX antenna 238 ofthe neural stimulator 114. In certain implementations, both the antenna110 and the RF pulse generator 106 are located subcutaneously. In otherimplementations, the antenna 110 and the RF pulse generator 106 arelocated external to the patient's body. In this case, the TX antenna 110may be coupled directly to the patient's skin.

Energy from the RF pulse generator is radiated to the implanted wirelessneural stimulator 114 from the antenna 110 through tissue, as shown inblock 304. The energy radiated may be controlled by thePatient/Clinician Parameter inputs in block 301. In some instances, theparameter settings can be adjusted in an open loop fashion by thepatient or clinician, who would adjust the parameter inputs in block 301to the system.

The wireless implanted stimulator 114 uses the received energy togenerate electrical pulses to be applied to the neural tissue throughthe electrodes 238. For instance, the stimulator 114 may containcircuitry that rectifies the received RF energy and conditions thewaveform to charge balance the energy delivered to the electrodes tostimulate the targeted nerves or tissues, as shown in block 306. Theimplanted stimulator 114 communicates with the pulse generator 106 byusing antenna 238 to send a telemetry signal, as shown in block 308. Thetelemetry signal may contain information about parameters of theelectrical pulses applied to the electrodes, such as the impedance ofthe electrodes, whether the safe current limit has been reached, or theamplitude of the current that is presented to the tissue from theelectrodes.

In block 310, the RF pulse generator 106 detects amplifies, filters andmodulates the received telemetry signal using amplifier 226, filter 224,and demodulator 222, respectively. The A/D converter 230 then digitizesthe resulting analog signal, as shown in 312. The digital telemetrysignal is routed to CPU 230, which determines whether the parameters ofthe signal sent to the stimulator 114 need to be adjusted based on thedigital telemetry signal. For instance, in block 314, the CPU 230compares the information of the digital signal to a look-up table, whichmay indicate an appropriate change in stimulation parameters. Theindicated change may be, for example, a change in the current level ofthe pulses applied to the electrodes. As a result, the CPU may changethe output power of the signal sent to stimulator 114 so as to adjustthe current applied by the electrodes 254, as shown in block 316.

Thus, for instance, the CPU 230 may adjust parameters of the signal sentto the stimulator 114 every cycle to match the desired current amplitudesetting programmed by the patient, as shown in block 318. The status ofthe stimulator system may be sampled in real time at a rate of 8 kbitsper second of telemetry data. All feedback data received from thestimulator 114 can be maintained against time and sampled per minute tobe stored for download or upload to a remote monitoring systemaccessible by the health care professional for trending and statisticalcorrelations in block 318. If operated in an open loop fashion, thestimulator system operation may be reduced to just the functionalelements shown in blocks 302, 304, 306, and 308, and the patient usestheir judgment to adjust parameter settings rather than the closedlooped feedback from the implanted device.

FIG. 4 depicts a flow chart showing an example of an operation of thesystem when the current level at the electrodes 254 is above a thresholdlimit. In certain instances, the implanted wireless neural stimulator114 may receive an input power signal with a current level above anestablished safe current limit, as shown in block 402. For instance, thecurrent limiter 248 may determine the current is above an establishedtissue-safe limit of amperes, as shown in block 404. If the currentlimiter senses that the current is above the threshold, it may stop thehigh-power signal from damaging surrounding tissue in contact with theelectrodes as shown in block 406, the operations of which are asdescribed above in association with FIGS. 2A and 2B.

A capacitor may store excess power, as shown in block 408. When thecurrent limiter senses the current is above the threshold, thecontroller 250 may use the excess power available to transmit a small2-bit data burst back to the RF pulse generator 106, as shown in block410. The 2-bit data burst may be transmitted through the implantedwireless neural stimulator's antenna(s) 238 during the RF pulsegenerator's receive cycle, as shown in block 412. The RF pulse generatorantenna 110 may receive the 2-bit data burst during its receive cycle,as shown in block 414, at a rate of 8 kbps, and may relay the data burstback to the RF pulse generator's feedback subsystem 212 which ismonitoring all reverse power, as shown in block 416. The CPU 230 mayanalyze signals from feedback subsystem 202, as shown in block 418 andif there is no data burst present, no changes may be made to thestimulation parameters, as shown in block 420. If the data burst ispresent in the analysis, the CPU 230 can cut all transmission power forone cycle, as shown in block 422.

If the data burst continues, the RF pulse generator 106 may push a“proximity power danger” notification to the application on theprogrammer module 102, as shown in block 424. This proximity dangernotification occurs because the RF pulse generator has ceased itstransmission of power. This notification means an unauthorized form ofenergy is powering the implant above safe levels. The application mayalert the user of the danger and that the user should leave theimmediate area to resume neural modulation therapy, as shown in block426. If after one cycle the data burst has stopped, the RF pulsegenerator 106 may slowly ramp up the transmission power in increments,for example from 5% to 75% of previous current amplitude levels, asshown in block 428. The user can then manually adjust current amplitudelevel to go higher at the user's own risk. During the ramp up, the RFpulse generator 106 may notify the application of its progress and theapplication may notify the user that there was an unsafe power level andthe system is ramping back up, as shown in block 430.

FIG. 5 is a diagram showing examples of signals that may be used todetect an impedance mismatch. As described above, a forward power signaland a reverse power signal may be used to detect an impedance mismatch.For instance, a RF pulse 502 generated by the RF pulse generator maypass through a device such as a dual directional coupler to the TXantenna 110. The TX antenna 110 then radiates the RF signal into thebody, where the energy is received by the implanted wireless neuralstimulator 114 and converted into a tissue-stimulating pulse. Thecoupler passes an attenuated version of this RF signal, forward power510, to feedback subsystem 212. The feedback subsystem 212 demodulatesthe AC signal and computes the amplitude of the forward RF power, andthis data is passed to controller subsystem 214. Similarly the dualdirectional coupler (or similar component) also receives RF energyreflected back from the TX antenna 110 and passes an attenuated versionof this RF signal, reverse power 512, to feedback subsystem 212. Thefeedback subsystem 212 demodulates the AC signal and computes theamplitude of the reflected RF power, and this data is passed tocontroller subsystem 214.

In the optimal case, when the TX antenna 110 may be perfectlyimpedance-matched to the body so that the RF energy passes unimpededacross the interface of the TX antenna 110 to the body, and no RF energyis reflected at the interface. Thus, in this optimal case, the reversepower 512 may have close to zero amplitude as shown by signal 504, andthe ratio of reverse power 512 to forward power 510 is zero. In thiscircumstance, no error condition exists, and the controller 214 sets asystem message that operation is optimal.

In practice, the impedance match of the TX antenna 204 to the body maynot be optimal, and some energy of the RF pulse 502 is reflected fromthe interface of the TX antenna 110 and the body. This can occur forexample if the TX antenna 110 is held somewhat away from the skin by apiece of clothing. This non-optimal antenna coupling causes a smallportion of the forward RF energy to be reflected at the interface, andthis is depicted as signal 506. In this case, the ratio of reverse power512 to forward power 510 is small, but a small ratio implies that mostof the RF energy is still radiated from the TX antenna 110, so thiscondition is acceptable within the control algorithm. This determinationof acceptable reflection ratio may be made within controller subsystem214 based upon a programmed threshold, and the controller subsystem 214may generate a low-priority alert to be sent to the user interface. Inaddition, the controller subsystem 214 sensing the condition of a smallreflection ratio, may moderately increase the amplitude of the RF pulse502 to compensate for the moderate loss of forward energy transfer tothe implanted wireless neural stimulator 114.

During daily operational use, the TX antenna 110 might be accidentallyremoved from the body entirely, in which case the TX antenna will havevery poor coupling to the body (if any). In this or other circumstances,a relatively high proportion of the RF pulse energy is reflected assignal 508 from the TX antenna 110 and fed backward into the RF-poweringsystem. Similarly, this phenomenon can occur if the connection to the TXantenna is physically broken, in which case virtually 100% of the RFenergy is reflected backward from the point of the break. In such cases,the ratio of reverse power 512 to forward power 510 is very high, andthe controller subsystem 214 will determine the ratio has exceeded thethreshold of acceptance. In this case, the controller subsystem 214 mayprevent any further RF pulses from being generated. The shutdown of theRF pulse generator module 106 may be reported to the user interface toinform the user that stimulation therapy cannot be delivered.

FIG. 6 is a diagram showing examples of signals that may be employedduring operation of the neural stimulator system. According to someimplementations, the amplitude of the RF pulse 602 received by theimplanted wireless neural stimulator 114 can directly control theamplitude of the stimulus 630 delivered to tissue. The duration of theRF pulse 608 corresponds to the specified pulse width of the stimulus630. During normal operation the RF pulse generator module 106 sends anRF pulse waveform 602 via TX antenna 110 into the body, and RF pulsewaveform 608 may represent the corresponding RF pulse received byimplanted wireless neural stimulator 114. In this instance the receivedpower has an amplitude suitable for generating a safe stimulus pulse630. The stimulus pulse 630 is below the safety threshold 626, and noerror condition exists. In another example, the attenuation between theTX antenna 110 and the implanted wireless neural stimulator 114 has beenunexpectedly reduced, for example due to the user repositioning the TXantenna 110. This reduced attenuation can lead to increased amplitude inthe RF pulse waveform 612 being received at the neural stimulator 114.Although the RF pulse 602 is generated with the same amplitude asbefore, the improved RF coupling between the TX antenna 110 and theimplanted wireless neural stimulator 114 can cause the received RF pulse612 to be larger in amplitude. Implanted wireless neural stimulator 114in this situation may generate a larger stimulus 632 in response to theincrease in received RF pulse 612. However, in this example, thereceived power 612 is capable of generating a stimulus 632 that exceedsthe prudent safety limit for tissue. In this situation, the currentlimiter feedback control mode can operate to clip the waveform of thestimulus pulse 632 such that the stimulus delivered is held within thepredetermined safety limit 626. The clipping event 628 may becommunicated through the feedback subsystem 212 as described above, andsubsequently controller subsystem 214 can reduce the amplitude specifiedfor the RF pulse. As a result, the subsequent RF pulse 604 is reduced inamplitude, and correspondingly the amplitude of the received RF pulse616 is reduced to a suitable level (non-clipping level). In thisfashion, the current limiter feedback control mode may operate to reducethe RF power delivered to the body if the implanted wireless neuralstimulator 114 receives excess RF power.

In another example, the RF pulse waveform 606 depicts a higher amplitudeRF pulse generated as a result of user input to the user interface. Inthis circumstance, the RF pulse 620 received by the implanted wirelessneural stimulator 14 is increased in amplitude, and similarly currentlimiter feedback mode operates to prevent stimulus 636 from exceedingsafety limit 626. Once again, this clipping event 628 may becommunicated through the feedback subsystem 212, and subsequentlycontroller subsystem 214 may reduce the amplitude of the RF pulse, thusoverriding the user input. The reduced RF pulse 604 can producecorrespondingly smaller amplitudes of the received waveforms 616, andclipping of the stimulus current may no longer be required to keep thecurrent within the safety limit. In this fashion, the current limiterfeedback may reduce the RF power delivered to the body if the implantedwireless neural stimulator 114 reports it is receiving excess RF power.

FIG. 7 is a flow chart showing a process for the user to control theimplantable wireless neural stimulator through the programmer in an openloop feedback system. In one implementation of the system, the user hasa wireless neural stimulator implanted in their body, the RF pulsegenerator 106 sends the stimulating pulse power wirelessly to thestimulator 114, and an application on the programmer module 102 (forexample, a smart device) is communicating with the RF pulse generator106. In this implementation, if a user wants to observe the currentstatus of the functioning pulse generator, as shown in block 702, theuser may open the application, as shown in block 704. The applicationcan use Bluetooth protocols built into the smart device to interrogatethe pulse generator, as shown in block 706. The RF pulse generator 106may authenticate the identity of the smart device and serialized patientassigned secure iteration of the application, as shown in block 708. Theauthentication process may utilize a unique key to the patient specificRF pulse generator serial number. The application can be customized withthe patient specific unique key through the Manufacturer Representativewho has programmed the initial patient settings for the stimulationsystem, as shown in block 720. If the RF pulse generator rejects theauthentication it may inform the application that the code is invalid,as shown in block 718 and needs the authentication provided by theauthorized individual with security clearance from the devicemanufacturer, known as the “Manufacturer's Representative,” as shown inblock 722. In an implementation, only the Manufacturer's Representativecan have access to the security code needed to change the application'sstored RF pulse generator unique ID. If the RF pulse generatorauthentication system passes, the pulse generator module 106 sends backall of the data that has been logged since the last sync, as shown inblock 710. The application may then register the most currentinformation and transmit the information to a 3rd party in a securefashion, as shown in 712. The application may maintain a database thatlogs all system diagnostic results and values, the changes in settingsby the user and the feedback system, and the global runtime history, asshown in block 714. The application may then display relevant data tothe user, as shown in block 716; including the battery capacity, currentprogram parameter, running time, pulse width, frequency, amplitude, andthe status of the feedback system.

FIGS. 8A and 8B show another example flow chart of a process for theuser to control the wireless stimulator with limitations on the lowerand upper limits of current amplitude. The user wants to change theamplitude of the stimulation signal, as shown in block 802. The user mayopen the application, as show in block 704 and the application may gothrough the process described in FIG. 7 to communicate with the RF pulsegenerator, authenticate successfully, and display the current status tothe user, as shown in block 804. The application displays thestimulation amplitude as the most prevalent changeable interface optionand displays two arrows with which the user can adjust the currentamplitude. The user may make a decision based on their need for more orless stimulation in accordance with their pain levels, as shown in block806. If the user chooses to increase the current amplitude, the user maypress the up arrow on the application screen, as shown in block 808. Theapplication can include safety maximum limiting algorithms, so if arequest to increase current amplitude is recognized by the applicationas exceeding the preset safety maximum, as shown in block 810, then theapplication will display an error message, as shown in block 812 andwill not communicate with the RF pulse generator module 106. If the userpresses the up arrow, as shown in block 808 and the current amplituderequest does not exceed the current amplitude maximum allowable value,then the application will send instructions to the RF pulse generatormodule 106 to increase amplitude, as shown in block 814. The RF pulsegenerator module 106 may then attempt to increase the current amplitudeof stimulation, as shown in block 816. If the RF pulse generator issuccessful at increasing the current amplitude, the RF pulse generatormodule 106 may perform a short vibration to physically confirm with theuser that the amplitude is increased, as shown in block 818. The RFpulse generator module 106 can also send back confirmation of increasedamplitude to the application, as shown in block 820, and then theapplication may display the updated current amplitude level, as shown inblock 822.

If the user decides to decrease the current amplitude level in block806, the user can press the down arrow on the application, as shown inblock 828. If the current amplitude level is already at zero, theapplication recognizes that the current amplitude cannot be decreasedany further, as shown in block 830 and displays an error message to theuser without communicating any data to the RF pulse generator, as shownin block 832. If the current amplitude level is not at zero, theapplication can send instructions to the RF pulse generator module 106to decrease current amplitude level accordingly, as shown in block 834.The RF pulse generator may then attempt to decrease current amplitudelevel of stimulation RF pulse generator module 106 and, if successful,the RF pulse generator module 106 may perform a short vibration tophysically confirm to the user that the current amplitude level has beendecreased, as shown in block 842. The RF pulse generator module 106 cansend back confirmation of the decreased current amplitude level to theapplication, as shown in block 838. The application then may display theupdated current amplitude level, as indicated by block 840. If thecurrent amplitude level decrease or increase fails, the RF pulsegenerator module 106 can perform a series of short vibrations to alertuser, and send an error message to the application, as shown in block824. The application receives the error and may display the data for theuser's benefit, as shown in block 826.

FIG. 9 is yet another example flow chart of a process for the user tocontrol the wireless neural stimulator 114 through preprogrammedparameter settings. The user wants to change the parameter program, asindicated by block 902. When the user is implanted with a wirelessneural stimulator or when the user visits the doctor, the Manufacturer'sRepresentative may determine and provide the patient/user RF pulsegenerator with preset programs that have different stimulationparameters that will be used to treat the user. The user will then ableto switch between the various parameter programs as needed. The user canopen the application on their smart device, as indicated by block 704,which first follows the process described in FIG. 7, communicating withthe RF pulse generator module 106, authenticating successfully, anddisplaying the current status of the RF pulse generator module 106,including the current program parameter settings, as indicated by block812. In this implementation, through the user interface of theapplication, the user can select the program that they wish to use, asshown by block 904. The application may then access a library ofpre-programmed parameters that have been approved by the Manufacturer'sRepresentative for the user to interchange between as desired and inaccordance with the management of their indication, as indicated byblock 906. A table can be displayed to the user, as shown in block 908and each row displays a program's codename and lists its basic parametersettings, as shown in block 910, which includes but is not limited to:pulse width, frequency, cycle timing, pulse shape, duration, feedbacksensitivity, as shown in block 912. The user may then select the rowcontaining the desired parameter preset program to be used, as shown inblock 912. The application can send instructions to the RF pulsegenerator module 106 to change the parameter settings, as shown in block916. The RF pulse generator module 106 may attempt to change theparameter settings 154. If the parameter settings are successfullychanged, the RF pulse generator module 106 can perform a uniquevibration pattern to physically confirm with the user that the parametersettings were changed, as shown in block 920. Also, the RF pulsegenerator module 106 can send back confirmation to the application thatthe parameter change has been successful, as shown in block 922, and theapplication may display the updated current program, as shown in block924. If the parameter program change has failed, the RF pulse generatormodule 106 may perform a series of short vibrations to alert the user,and send an error message to the application, as shown in block 926,which receives the error and may display to the user, as shown in block928.

FIG. 10 is still another example flow chart of a process for a lowbattery state for the RF pulse generator module 106. In thisimplementation, the RF pulse generator module's remaining battery powerlevel is recognized as low, as shown in block 1002. The RF pulsegenerator module 106 regularly interrogates the power supply batterysubsystem 210 about the current power and the RF pulse generatormicroprocessor asks the battery if its remaining power is belowthreshold, as shown in block 1004. If the battery's remaining power isabove the threshold, the RF pulse generator module 106 may store thecurrent battery status to be sent to the application during the nextsync, as shown in block 1006. If the battery's remaining power is belowthreshold the RF pulse generator module 106 may push a low-batterynotification to the application, as shown in block 1008. The RF pulsegenerator module 106 may always perform one sequence of short vibrationsto alert the user of an issue and send the application a notification,as shown in block 1010. If there continues to be no confirmation of theapplication receiving the notification then the RF pulse generator cancontinue to perform short vibration pulses to notify user, as shown inblock 1010. If the application successfully receives the notification,it may display the notification and may need user acknowledgement, asshown in block 1012. If, for example, one minute passes without thenotification message on the application being dismissed the applicationinforms the RF pulse generator module 106 about lack of humanacknowledgement, as shown in block 1014, and the RF pulse generatormodule 106 may begin to perform the vibration pulses to notify the user,as shown in block 1010. If the user dismisses the notification, theapplication may display a passive notification to switch the battery, asshown in block 1016. If a predetermined amount of time passes, such asfive minutes for example, without the battery being switched, theapplication can inform the RF pulse generator module 106 of the lack ofhuman acknowledgement, as shown in block 1014 and the RF pulse generatormodule 106 may perform vibrations, as shown in block 1010. If the RFpulse generator module battery is switched, the RF pulse generatormodule 106 reboots and interrogates the battery to assess powerremaining, as shown in block 1018. If the battery's power remaining isbelow threshold, the cycle may begin again with the RF pulse generatormodule 106 pushing a notification to the application, as shown in block1008. If the battery's power remaining is above threshold the RF pulsegenerator module 106 may push a successful battery-change notificationto the application, as shown in block 1020. The application may thencommunicate with the RF pulse generator module 106 and displays currentsystem status, as shown in block 1022.

FIG. 11 is yet another example flow chart of a process for aManufacturer's Representative to program the implanted wireless neuralstimulator. In this implementation, a user wants the Manufacturer'sRepresentative to set individual parameter programs from a remotelocation different than where the user is, for the user to use asneeded, as shown in block 1102. The Manufacturer's Representative cangain access to the user's set parameter programs through a secure webbased service. The Manufacturer's Representative can securely log intothe manufacturer's web service on a device connected to the Internet, asshown in block 1104. If the Manufacturer's Representative is registeringthe user for the first time in their care they enter in the patient'sbasic information, the RF pulse generator's unique ID and theprogramming application's unique ID, as shown in block 1106. Once theManufacturer's Representative's new or old user is already registered,the Manufacturer's Representative accesses the specific user's profile,as shown in block 1108. The Manufacturer's Representative is able toview the current allotted list of parameter programs for the specificuser, as shown in block 1110. This list may contain previous active andretired parameter preset programs, as shown in block 1112. TheManufacturer's Representative is able to activate/deactivate presetparameter programs by checking the box next to the appropriate row inthe table displayed, as shown in block 1114. The Manufacturer'sRepresentative may then submit and save the allotted new presetparameter programs, as shown in block 1116. The user's programmerapplication may receive the new preset parameter programs at the nextsync with the manufacturer's database.

FIG. 12 is a circuit diagram showing an example of a wireless neuralstimulator, such as stimulator 114. This example contains pairedelectrodes, comprising cathode electrode(s) 1208 and anode electrode(s)1210, as shown. When energized, the charged electrodes create a volumeconduction field of current density within the tissue. In thisimplementation, the wireless energy is received through a dipoleantenna(s) 238. At least four diodes are connected together to form afull wave bridge rectifier 1202 attached to the dipole antenna(s) 238.Each diode, up to 100 micrometers in length, uses a junction potentialto prevent the flow of negative electrical current, from cathode toanode, from passing through the device when said current does not exceedthe reverse threshold. For neural stimulation via wireless power,transmitted through tissue, the natural inefficiency of the lossymaterial may lead to a low threshold voltage. In this implementation, azero biased diode rectifier results in a low output impedance for thedevice. A resistor 1204 and a smoothing capacitor 1206 are placed acrossthe output nodes of the bridge rectifier to discharge the electrodes tothe ground of the bridge anode. The rectification bridge 1202 includestwo branches of diode pairs connecting an anode-to-anode and thencathode to cathode. The electrodes 1208 and 1210 are connected to theoutput of the charge balancing circuit 246.

FIG. 13 is a circuit diagram of another example of a wireless neuralstimulator, such as stimulator 114. The example shown in FIG. 13includes multiple electrode control and may employ full closed loopcontrol. The stimulator includes an electrode array 254 in which thepolarity of the electrodes can be assigned as cathodic or anodic, andfor which the electrodes can be alternatively not powered with anyenergy. When energized, the charged electrodes create a volumeconduction field of current density within the tissue. In thisimplementation, the wireless energy is received by the device throughthe dipole antenna(s) 238. The electrode array 254 is controlled throughan on-board controller circuit 242 that sends the appropriate bitinformation to the electrode interface 252 in order to set the polarityof each electrode in the array, as well as power to each individualelectrode. The lack of power to a specific electrode would set thatelectrode in a functional OFF position. In another implementation (notshown), the amount of current sent to each electrode is also controlledthrough the controller 242. The controller current, polarity and powerstate parameter data, shown as the controller output, is be sent back tothe antenna(s) 238 for telemetry transmission back to the pulsegenerator module 106. The controller 242 also includes the functionalityof current monitoring and sets a bit register counter so that the statusof total current drawn can be sent back to the pulse generator module106.

At least four diodes can be connected together to form a full wavebridge rectifier 302 attached to the dipole antenna(s) 238. Each diode,up to 100 micrometers in length, uses a junction potential to preventthe flow of negative electrical current, from cathode to anode, frompassing through the device when said current does not exceed the reversethreshold. For neural stimulation via wireless power, transmittedthrough tissue, the natural inefficiency of the lossy material may leadto a low threshold voltage. In this implementation, a zero biased dioderectifier results in a low output impedance for the device. A resistor1204 and a smoothing capacitor 1206 are placed across the output nodesof the bridge rectifier to discharge the electrodes to the ground of thebridge anode. The rectification bridge 1202 may include two branches ofdiode pairs connecting an anode-to-anode and then cathode to cathode.The electrode polarity outputs, both cathode 1208 and anode 1210 areconnected to the outputs formed by the bridge connection. Chargebalancing circuitry 246 and current limiting circuitry 248 are placed inseries with the outputs.

FIG. 14 is a block diagram showing an example of control functions 1405and feedback functions 1430 of a wireless implantable neural stimulator1400, such as the ones described above or further below. An exampleimplementation of the implantable neural stimulator 1400 may beimplanted lead module 114, as discussed above in association with FIG.2. Control functions 1405 include functions 1410 for polarity switchingof the electrodes and functions 1420 for power-on reset.

Polarity switching functions 1410 may employ, for example, a polarityrouting switch network to assign polarities to electrodes 254. Theassignment of polarity to an electrode may, for instance, be one of: acathode (negative polarity), an anode (positive polarity), or a neutral(off) polarity. The polarity assignment information for each of theelectrodes 254 may be contained in the input signal received by wirelessimplantable neural stimulator 1400 through Rx antenna 238 from RF pulsegenerator module 106. Because a programmer module 102 may control RFpulse generator module 106, the polarity of electrodes 254 may becontrolled remotely by a programmer through programmer module 102, asshown in FIGS. 2A and 2B.

Power-on reset functions 1420 may reset the polarity assignment of eachelectrode immediately on each power-on event. As will be described infurther detail below, this reset operation may cause RF pulse generatormodule 106 to transmit the polarity assignment information to thewireless implantable neural stimulator 1400. Once the polarityassignment information is received by the wireless implantable neuralstimulator 1400, the polarity assignment information may be stored in aregister file, or other short term memory component. Thereafter thepolarity assignment information may be used to configure the polarityassignment of each electrode. If the polarity assignment informationtransmitted in response to the reset encodes the same polarity state asbefore the power-on event, then the polarity state of each electrode canbe maintained before and after each power-on event.

Feedback functions 1430 include functions 1440 for monitoring deliveredpower to electrodes 254 and functions 1450 for making impedancediagnosis of electrodes 254. For example, delivered power functions 1440may provide data encoding the amount of power being delivered fromelectrodes 254 to the excitable tissue and tissue impedance diagnosticfunctions 1450 may provide data encoding the diagnostic information oftissue impedance. The tissue impedance is the electrical impedance ofthe tissue as seen between negative and positive electrodes when astimulation current is being released between negative and positiveelectrodes.

Feedback functions 1430 may additionally include tissue depth estimatefunctions 1460 to provide data indicating the overall tissue depth thatthe input radio frequency (RF) signal from the pulse generator module,such as, for example, RF pulse generator module 106, has penetratedbefore reaching the implanted antenna, such as, for example, RX antenna238, within the wireless implantable neural stimulator 1400, such as,for example, implanted lead module 114. For instance, the tissue depthestimate may be provided by comparing the power of the received inputsignal to the power of the RF pulse transmitted by the RF pulsegenerator 106. The ratio of the power of the received input signal tothe power of the RF pulse transmitted by the RF pulse generator 106 mayindicate an attenuation caused by wave propagation through the tissue.For example, the second harmonic described below may be received by theRF pulse generator 106 and used with the power of the input signal sentby the RF pulse generator to determine the tissue depth. The attenuationmay be used to infer the overall depth of wireless implantable neuralstimulator 1400 underneath the skin.

The data from blocks 1440, 1450, and 1460 may be transmitted, forexample, through Tx antenna 110 to RF pulse generator 106, asillustrated in FIGS. 1 and 2.

As discussed above in association with FIGS. 1, 2, 12, and 13, awireless implantable neural stimulator 1400 may utilize rectificationcircuitry to convert the input signal (e.g., having a carrier frequencywithin a range from about 800 MHz to about 6 GHz) to a direct current(DC) power to drive the electrodes 254. Some implementations may providethe capability to regulate the DC power remotely. Some implementationsmay further provide different amounts of power to different electrodes,as discussed in further detail below.

FIG. 15 is a schematic showing an example of a wireless implantableneural stimulator 1500 with components to implement control and feedbackfunctions as discussed above in association with FIG. 14. An RX antenna1505 receives the input signal. The RX antenna 1505 may be embedded as adipole, microstrip, folded dipole or other antenna configuration otherthan a coiled configuration, as described above. The input signal has acarrier frequency in the GHz range and contains electrical energy forpowering the wireless implantable neural stimulator 1500 and forproviding stimulation pulses to electrodes 254. Once received by theantenna 1505, the input signal is routed to power management circuitry1510. Power management circuitry 1510 is configured to rectify the inputsignal and convert it to a DC power source. For example, the powermanagement circuitry 1510 may include a diode rectification bridge suchas the diode rectification bridge 1202 illustrated in FIG. 12. The DCpower source provides power to stimulation circuitry 1511 and logicpower circuitry 1513. The rectification may utilize one or more fullwave diode bridge rectifiers within the power management circuitry 1510.In one implementation, a resistor can be placed across the output nodesof the bridge rectifier to discharge the electrodes to the ground of thebridge anode, as illustrated by the shunt register 1204 in FIG. 12.

FIG. 16 shows an example pulse waveform generated by the MFS sent to thepower management circuitry 1510 of the wireless implantable neuralstimulator 1500. This can be a typical pulse waveform generated by theRF pulse generator module 106 and then passed on the carrier frequency.The pulse amplitude is ramped over the pulse width (duration) from avalue ranging from −9 dB to +6 dB. In certain implementations, the rampstart and end power level can be set to any range from 0 to 60 dB. Thegain control is adjustable and can be an input parameter from RF pulsegenerator module 106 to the stimulation power management circuitry 1510.The pulse width, Pw, can range from 100 to 300 microseconds (μs) in someimplementations, as shown in FIG. 16. In other implementations notshown, the pulse width can be between about 5 microseconds (5 us) andabout 10 milliseconds (10 ms). The pulse frequency (rate) can range fromabout 5 Hz to 120 Hz as shown. In some implementations not shown, thepulse frequency can be below 5 Hz, and as high as about 10,000 Hz.

Returning to FIG. 15, based on the received waveform, stimulationcircuitry 1511 creates the stimulation waveform to be sent to theelectrodes 254 to stimulate excitable tissues, as discussed above. Insome implementations, stimulation circuitry 1511 may route the waveformto pulse-shaping resistor-capacitor (RC) timer 1512 to shape eachtravelling pulse waveform. An example RC-timer can be the shunt resistor1204 and smoothing resistor 1206, as illustrated in FIG. 12 and asdiscussed above. The pulse-shaping RC timer 1512 can also be used to,but is not limited to, inverting the pulse to create a pre-anodic dip orprovide a slow ramping in waveform.

Once the waveform has been shaped, the cathodic energy—energy beingtransmitted over the cathodic branch 1515 of the polarity routing switchnetwork 1523—is routed through the passive charge balancing circuitry1518 to prevent the build-up of noxious chemicals at the electrodes 254,as discussed above. Cathodic energy is then routed to input 1, block1522, of polarity routing switch network 1521. Anodic energy—energybeing transmitted over the anodic branch 1514 of the polarity routingswitch network 1523—is routed to input 2, block 1523, of polarityrouting switch network 1521. Thereafter, the polarity routing switchnetwork 1521 delivers the stimulation energy in the form of cathodicenergy, anodic energy, or no energy, to the each of the electrodes 254,depending on the respective polarity assignment, which is controlledbased on a set of bits stored in the register file 1532. The bits storedin the register file 1532 are output to a selection input 1534 of thepolarity routing switch network 1523, which causes input 1 or input 2 tobe routed to the electrodes as appropriate.

Turning momentarily to FIG. 17, a schematic of an example of a polarityrouting switch network 1700 is shown. As discussed above, the cathodic(−) energy and the anodic energy are received at input 1 (block 1522)and input 2 (block 1523), respectively. Polarity routing switch network1700 has one of its outputs coupled to an electrode of electrodes 254which can include as few as two electrodes, or as many as sixteenelectrodes. Eight electrodes are shown in this implementation as anexample.

Polarity routing switch network 1700 is configured to eitherindividually connect each output to one of input 1 or input 2, ordisconnect the output from either of the inputs. This selects thepolarity for each individual electrode of electrodes 254 as one of:neutral (off), cathode (negative), or anode (positive). Each output iscoupled to a corresponding three-state switch 1730 for setting theconnection state of the output. Each three-state switch is controlled byone or more of the bits from the selection input 1750. In someimplementations, selection input 1750 may allocate more than one bits toeach three-state switch. For example, two bits may encode thethree-state information. Thus, the state of each output of polarityrouting switch device 1700 can be controlled by information encoding thebits stored in the register 1532, which may be set by polarityassignment information received from the remote RF pulse generatormodule 106, as described further below.

Returning to FIG. 15, power and impedance sensing circuitry may be usedto determine the power delivered to the tissue and the impedance of thetissue. For example, a sensing resistor 1518 may be placed in serialconnection with the anodic branch 1514. Current sensing circuit 1519senses the current across the resistor 1518 and voltage sensing circuit1520 senses the voltage across the resistor. The measured current andvoltage may correspond to the actual current and voltage applied by theelectrodes to the tissue.

As described below, the measured current and voltage may be provided asfeedback information to RF pulse generator module 106. The powerdelivered to the tissue may be determined by integrating the product ofthe measured current and voltage over the duration of the waveform beingdelivered to electrodes 254. Similarly, the impedance of the tissue maybe determined based on the measured voltage being applied to theelectrodes and the current being applied to the tissue. Alternativecircuitry (not shown) may also be used in lieu of the sensing resistor1518, depending on implementation of the feature and whether bothimpedance and power feedback are measured individually, or combined.

The measurements from the current sensing circuitry 1519 and the voltagesensing circuitry 1520 may be routed to a voltage controlled oscillator(VCO) 1533 or equivalent circuitry capable of converting from an analogsignal source to a carrier signal for modulation. VCO 1533 can generatea digital signal with a carrier frequency. The carrier frequency mayvary based on analog measurements such as, for example, a voltage, adifferential of a voltage and a power, etc. VCO 1533 may also useamplitude modulation or phase shift keying to modulate the feedbackinformation at the carrier frequency. The VCO or the equivalent circuitmay be generally referred to as an analog controlled carrier modulator.The modulator may transmit information encoding the sensed current orvoltage back to RF pulse generator 106.

Antenna 1525 may transmit the modulated signal, for example, in the GHzfrequency range, back to the RF pulse generator module 106. In someembodiments, antennas 1505 and 1525 may be the same physical antenna. Inother embodiments, antennas 1505 and 1525 may be separate physicalantennas. In the embodiments of separate antennas, antenna 1525 mayoperate at a resonance frequency that is higher than the resonancefrequency of antenna 1505 to send stimulation feedback to RF pulsegenerator module 106. In some embodiments. antenna 1525 may also operateat the higher resonance frequency to receive data encoding the polarityassignment information from RF pulse generator module 106.

Antenna 1525 may be a telemetry antenna 1525 which may route receiveddata, such as polarity assignment information, to the stimulationfeedback circuit 1530. The encoded polarity assignment information maybe on a band in the GHz range. The received data may be demodulated bydemodulation circuitry 1531 and then stored in the register file 1532.The register file 1532 may be a volatile memory. Register file 1532 maybe an 8-channel memory bank that can store, for example, several bits ofdata for each channel to be assigned a polarity. Some embodiments mayhave no register file, while some embodiments may have a register fileup to 64 bits in size. The information encoded by these bits may be sentas the polarity selection signal to polarity routing switch network1521, as indicated by arrow 1534. The bits may encode the polarityassignment for each output of the polarity routing switch network as oneof: +(positive), −(negative), or 0 (neutral). Each output connects toone electrode and the channel setting determines whether the electrodewill be set as an anode (positive), cathode (negative), or off(neutral).

Returning to power management circuitry 1510, in some embodiments,approximately 90% of the energy received is routed to the stimulationcircuitry 1511 and less than 10% of the energy received is routed to thelogic power circuitry 1513. Logic power circuitry 1513 may power thecontrol components for polarity and telemetry. In some implementations,the power circuitry 1513, however, does not provide the actual power tothe electrodes for stimulating the tissues. In certain embodiments, theenergy leaving the logic power circuitry 1513 is sent to a capacitorcircuit 1516 to store a certain amount of readily available energy. Thevoltage of the stored charge in the capacitor circuit 1516 may bedenoted as Vdc. Subsequently, this stored energy is used to power apower-on reset circuit 1516 configured to send a reset signal on apower-on event. If the wireless implantable neural stimulator 1500 losespower for a certain period of time, for example, in the range from about1 millisecond to over 10 milliseconds, the contents in the register file1532 and polarity setting on polarity routing switch network 1521 may bezeroed. The wireless implantable neural stimulator 1500 may lose power,for example, when it becomes less aligned with RF pulse generator module106. Using this stored energy, power-on reset circuit 1540 may provide areset signal as indicated by arrow 1517. This reset signal may causestimulation feedback circuit 1530 to notify RF pulse generator module106 of the loss of power. For example, stimulation feedback circuit 1530may transmit a telemetry feedback signal to RF pulse generator module106 as a status notification of the power outage. This telemetryfeedback signal may be transmitted in response to the reset signal andimmediately after power is back on neural stimulator 1500. RF pulsegenerator module 106 may then transmit one or more telemetry packets toimplantable wireless neutral stimulator. The telemetry packets containpolarity assignment information, which may be saved to register file1532 and may be sent to polarity routing switch network 1521. Thus,polarity assignment information in register file 1532 may be recoveredfrom telemetry packets transmitted by RF pulse generator module 106 andthe polarity assignment for each output of polarity routing switchnetwork 1521 may be updated accordingly based on the polarity assignmentinformation.

The telemetry antenna 1525 may transmit the telemetry feedback signalback to RF pulse generator module 106 at a frequency higher than thecharacteristic frequency of an RX antenna 1505. In one implementation,the telemetry antenna 1525 can have a heightened resonance frequencythat is the second harmonic of the characteristic frequency of RXantenna 1505. For example, the second harmonic may be utilized totransmit power feedback information regarding an estimate of the amountof power being received by the electrodes. The feedback information maythen be used by the RF pulse generator in determining any adjustment ofthe power level to be transmitted by the RF pulse generator 106. In asimilar manner, the second harmonic energy can be used to detect thetissue depth. The second harmonic transmission can be detected by anexternal antenna, for example, on RF pulse generator module 106 that istuned to the second harmonic. As a general matter, power managementcircuitry 1510 may contain rectifying circuits that are non-lineardevice capable of generating harmonic energies from input signal.Harvesting such harmonic energy for transmitting telemetry feedbacksignal could improve the efficiency of wireless implantable neuralstimulator 1500. FIGS. 18A and 18B and the following discussiondemonstrate the feasibility of utilizing the second harmonic to transmittelemetry signal to RF pulse generator module 106.

FIGS. 18A and 18BB respectively show an example full-wave rectified sinewave and the corresponding spectrum. In particular, a full-waverectified 915 MHz sine wave is being analyzed. In this example, thesecond harmonic of a 915 MHz sine wave is an 1830 MHz output harmonic.This harmonic wave may be attenuated by the amount of tissue that theharmonic wave needs to pass through before reaching the externalharmonic receiver antenna. In general, an estimation of the power levelsduring the propagation of the harmonic wave can reveal the feasibilityof the approach. The estimation may consider the power of received inputsignal at the receiving antenna (e.g., at antenna 1505 and at 915 MHz),the power of the second harmonic radiated from the rectified 915 MHzwaveform, the amount of attenuation for the second harmonic wave topropagate through the tissue medium, and an estimation of the couplingefficiency for the harmonic antenna. The average power transmitted inWatts can be estimated by Equation 1:Pt=Pk DuCP _(r)=(P _(t) /A _(ant))(1−{Γ}²)Lλ ² G _(r)η/4π)  (1)

Table 1 below tabulates the denotations of each symbol and thecorresponding value used in the estimation.

TABLE 1 Parameters utilized in development of the Received Powerequation. Parameter Value P_(k) (PeakPower)(W) 1.576 DuC (Duty Cycle)0.5 P_(t) (Average power transmitted) 1.576 A_(ant) (Antenna aperturearea) (m²) 0.01 Γ (Voltage reflection coefficient) 0.5 1 − {Γ}²(Transmission Loss) 0.75 L (Loss through tissue) (dB) 10 λ (Wavelength)(m) 0.689 G_(r) (Gain of implanted receiving antenna) 2 η (RF-DCefficiency) 0.5 R_(torso)(Equivalent Tissue Resistance) (Ohm) 500

In estimating L, the loss due to the attenuation in the tissue,attentions from the fundamental (for the forward path to the implantedlead module 114) and second harmonics (for the reverse path from theimplanted lead module 113) may be considered. The plane wave attenuationis given by the following equation (2) and Table 2:

$\begin{matrix}{{\alpha = {\frac{2\pi\; f}{c}\left( \frac{ɛ_{r}}{2} \right)^{0.5}\left( {{- 1} + \left( {1 + \left( \frac{\sigma}{{\varpi ɛ}_{0}ɛ_{r}} \right)^{2}} \right)^{0.5}} \right)^{0.5}}}{where}{f = {frequency}}{c = {{speed}\mspace{14mu}{of}\mspace{14mu}{light}\mspace{14mu}{in}\mspace{14mu}{vacuum}}}{ɛ_{r} = {{relative}\mspace{14mu}{dielectric}\mspace{14mu}{constant}}}{\sigma = {conductivity}}{ɛ_{0} = {{permittivity}\mspace{14mu}{of}\mspace{14mu}{vacuum}}}} & (2)\end{matrix}$

TABLE 2 Estimated output power loss for 915 MHz and 1830 MHz harmonic at1 cm depth. Freq(MHz) _(r) S/m) neper/m) Power loss 0.915e9 41.3290.87169 25.030 0.606 1.83e9  38.823 1.1965 35.773 0.489

The worst-case assumption for coupling of the harmonics wave to theexternal receive antenna is that the power radiated at the harmonicfrequency by the implanted telemetry antenna (e.g., telemetry antenna1625) is completely absorbed by external receive antenna. Thisworse-case scenario can be modeled by the following equation (3) andTable 3:P_(nr=P) _(t)L_(n)L_(na)  (3)

where

n=nth Harmonic

P_(nr)=nth Harmonic Antenna Received Power (W)

P_(t)=Total Received power of Implant(W)

L_(n)=Power of nth Harmonic of Implant Power(W)

L_(na)=Attenuation Loss Factor

TABLE 3 Output total power and received harmonic power for the 2^(nd)harmonic. P_(t)(W) L_(n) L_(na) P_(nr)(W) dBm 0.356 .2421 0.489 0.042216.3

In sum, the reduction of power levels has been estimated to be about 10dB utilizing these developed equations. This includes the attenuation ofa 915 MHz plane wave that propagates through tissue depths from 1 cm to6 cm. The average received power, Pr, at 915 MHz is 0.356 W. The powerin the second harmonic (1830 MHz) is about −6.16 dB, as obtained from aSPICE simulation using a full wave rectified 915 MHz sine wave. Theestimate of 10 dB means a reduction of a factor of 10, which isacceptable for field operations. Thus, the feasibility of utilizing thesecond harmonic frequency to transmit the telemetry feedback signal backto the RF pulse generator module 106 has been demonstrated.

FIG. 19 is a flow chart illustrating an example of operations of controland feedback functions of the neural stimulator. The operations aredescribed with respect to the wireless implantable neural stimulator1500, although the operations may be performed by other variations of awireless implantable neural stimulator, such as the ones describedabove.

RF pulse generator module 106 transmits one or more signals containingelectrical energy (1900). RF pulse generator module 106 may also beknown as a microwave field stimulator (MFS) in some implementations. Thesignal may be modulated at a microwave frequency band, for example, fromabout 800 MHz to about 6 GHz.

The input signal containing electrical energy is received by RX antenna1505 of the neural stimulator 1500 (1910). As discussed above, RXantenna 1505 may be embedded as a dipole, microstrip, folded dipole orother antenna configuration other than a coiled configuration.

The input signal is rectified and demodulated by the power managementcircuitry 1510, as shown by block 1911. Some implementations may providewaveform shaping and, in this case, the rectified and demodulated signalis passed to pulse shaping RC timer (1912). Charge balancing may beperformed by charge balancing circuit 1518 to provide a charged balancedwaveform (1913). Thereafter, the shaped and charge balanced pulses arerouted to electrodes 254 (1920), which deliver the stimulation to theexcitable tissue (1921).

In the meantime, the current and voltage being delivered to the tissueis measured using the current sensor 1519 and voltage sensor 1520(1914). These measurements are modulated and amplified (1915) andtransmitted to the RF pulse generator module 106 from telemetry antenna1525 (1916). In some embodiments, the telemetry antenna 1525 and RXantenna 1505 may utilize the same physical antenna embedded within theneural stimulator 1500. The RF pulse generator module 106 may use themeasured current and voltage to determine the power delivered to thetissue, as well as the impedance of the tissue.

For example, the RF pulse generator module 106 may store the receivedfeedback information such as the information encoding the current andvoltage. The feedback information may be stored, for instance, as apresent value in a hardware memory on RF pulse generator module 106.Based on the feedback information, RF pulse generator module 106 maycalculate the impedance value of the tissue based on the current andvoltage delivered to the tissue.

In addition, RF pulse generator module 106 may calculate the powerdelivered to the tissue based on the stored current and voltage (1950).The RF pulse generator module 106 can then determine whether power levelshould be adjusted by comparing the calculated power to the desiredpower stored, for example, in a lookup table stored on the RF pulsegenerator module 106 (1917). For example, the look-up table may tabulatethe optimal amount of power that should be delivered to the tissue forthe position of the receive antenna 1505 on neural stimulator 1500relative to the position of the transmit antenna on RF pulse generatormodule 106. This relative position may be determined based on thefeedback information. The power measurements in the feedback informationmay then be correlated to the optimal value to determine if a powerlevel adjustment should be made to increase or decrease the amplitude ofstimulation of the delivered power to the electrodes. The power leveladjustment information may then enable the RF pulse generator module 106to adjust parameters of transmission so that the adjusted power isprovided to the RX antenna 1505.

In addition to the input signal containing electrical energy forstimulation, the RF pulse generator module 106 may send an input signalthat contains telemetry data such as polarity assignment information(1930). For instance, upon power on, the RF pulse generator module 106may transmit data encoding the last electrode polarity settings for eachelectrode before RF pulse generator module 106 was powered off. Thisdata may be sent to telemetry antenna 1525 as a digital data streamembedded on the carrier waveform. In some implementations, the datastream may include telemetry packets. The telemetry packets are receivedfrom the RF pulse generator module 106 and subsequently demodulated(1931) by demodulation circuit 1531. The polarity setting information inthe telemetry packets is stored in the register file 1532 (1932). Thepolarity of each electrode of electrodes 254 is programmed according tothe polarity setting information stored in the register file 1532(1933). For example, the polarity of each electrode may be set as oneof: anode (positive), cathode (negative), or neutral (off).

As discussed above, upon a power-on reset, the polarity settinginformation is resent from the RF pulse generator module 106 to bestored in the register file 1532 (1932). This is indicated by the arrow1932 to 1916. The information of polarity setting stored in the registerfile 1532 may then be used to program the polarity of each electrode ofelectrodes 254 (1933). The feature allows for re-programming of apassive device remotely from the RF pulse generator module 106 at thestart of each powered session, thus obviating the need of maintainingCMOS memory within the neural stimulator 1500.

FIG. 20A is a diagram of an example implementation of a microwave fieldstimulator (MFS) 2002 as part of a stimulation system utilizing animplantable, passive device 2022. In this example, the MFS 2002 isexternal to a patient's body and may be placed within in closeproximity, for example, within 3 feet, to an implantable, passive 2022.The RF pulse generator module 106 may be one example implementation ofMFS 2002. MFS 2002 may be generally known as a controller module. Theimplanted lead module 114 may be one example of an implantable, passivesimulation device 2022. The implantable, passive simulation device 2022is a passive device. The implantable, passive stimulation device doesnot have its own independent power source, rather it receives power forits operation from transmission signals emitted from a TX antennapowered by the MFS 2002, as discussed above.

In certain embodiments, the MFS 2002 may communicate with a programmer2012. The programmer 2012 may be a mobile computing device, such as, forexample, a laptop, a smart phone, a tablet, etc. The communication maybe wired, using for example, a USB or firewire cable. The communicationmay also be wireless, utilizing for example, a bluetooth protocolimplemented by a transmitting blue tooth module 2004 which communicateswith the host bluetooth module 2014 within the programmer 2012. A user,such as a patient, company representative, or a doctor may use theprogrammer 2012 to send stimulation information to the MFS 2012, whichstores the stimulation information. The stimulation information mayinclude, for example, the polarity of the electrodes in the implantable,passive stimulation device 2022 and/or the parameters defining thestimulation waveform.

The MFS 2002 may additionally communicate with implantable, passivestimulation device 2022 by transmitting a transmission signal through aTX antenna 2007 coupled to an amplifier 2006. The transmission signalmay propagate through skin and underlying tissues to arrive at the RXantenna 2023 of the implantable, passive stimulation device 2022. Asdiscussed in further detail below, this transmission signal may encodepolarity assignments for the electrodes in the stimulation device 2022and include the stimulation waveform. In some implementations, theimplantable, passive stimulation device 2022 may transmit a telemetryfeedback signal back to MFS 2002.

The MFS 2002 may include a microcontroller 2008 configured to manage thecommunication with a programmer 2012 and generate an output signal basedon the stimulation information sent from the programmer. The outputsignal may be used by the modulator 2009 to modulate a RF carrier signalto generate the transmission signal. The frequency of the carrier signalmay be in the microwave range, for example, from about 300 MHz to about8 GHz. This frequency may be known as the stimulus carrier frequency.The modulated RF carrier signal may be amplified by an amplifier 2006 toprovide the transmission signal for transmission to the implantable,passive stimulation device 2022 through a TX antenna 2007.

FIG. 20B is a diagram of another example of an implementation of amicrowave field stimulator 2002 as part of a stimulation systemutilizing an implantable, passive neural stimulator 2022. In thisexample, the MFS 2002 may be embedded in the body of the patient, forexample, subcutaneously. The embedded MFS 2002 may receive power from adetached, remote wireless battery charger 2032.

The power from the wireless battery charger 2032 to the embedded MFS2002 may be transmitted at a frequency in the MHz or GHz range and viainductive coupling. The MFS 2002 may be embedded subcutaneously at avery shallow depth (e.g., less than 1 cm), inductive coupling totransfer energy from wireless battery charger 2032 to the embedded MFS2002 may be feasible and efficient.

In some embodiments, the MFS 2002 may be adapted for placement at theepidural layer of a spinal column, near or on the dura of the spinalcolumn, in tissue in close proximity to the spinal column, in tissuelocated near a dorsal horn, in dorsal root ganglia, in one or more ofthe dorsal roots, in dorsal column fibers, or in peripheral nervebundles leaving the dorsal column of the spine.

In this embodiment, the MFS 2002 may transmit power and parametersignals to a passive TX antenna also embedded subcutaneously, which maybe coupled to the RX antenna within the implanted, passive stimulationdevice. The power required in this embodiment is substantially lowersince the TX antenna and the RX antenna are already in body tissue andthere is no requirement to transmit the signal through the skin.

FIG. 21 is a detailed diagram of an example microwave field stimulator2002. A microwave field stimulator 2002 may include a microcontroller2008, a telemetry feedback module 2102, and a power management module2104. A MFS 2002 has a two-way communication schema with a programmer2012, as well as with a communication or telemetry antenna 2106. A MFSsends output power and data signals through a TX antenna 2108.

The microcontroller 2008 may include a storage device 2114, a bluetoothinterface 2113, a USB interface 2112, a power interface 2111, an Analogto Digital convertor (ADC) 2116, and a Digital to Analog convertor (DAC)2115. Implementations of a storage device 2114 may include non-volatilememory, such as, for example, static electrically erasable programmableread-only memory (SEEPROM) or NAND flash memory. A storage device 2114may store waveform parameter information for the microcontroller 2008 tosynthesize the output signal used by modulator 2009. The stimulationwaveform may include multiple pulses. The waveform parameter informationmay include the shape, duration, amplitude of each pulse, as well aspulse repetition frequency. A storage device 2114 may additionally storepolarity assignment information for each electrode of implantable,passive neural stimulation device 2022. The Bluetooth interface 2113 andUSB interface 2112 respectively interact with either the bluetoothmodule 2004 or the USB module to communicate with the programmer 2012.

The communication antenna 2106 and a TX antenna 2108 may, for example,be configured in a variety of sizes and form factors, including, but notlimited to a patch antenna, a slot antenna, or a dipole antenna. The TXantenna 2108 may be adapted to transmit a transmission signal to theimplantable, passive neural stimulation device 2022. As discussed above,an output signal generated by the microcontroller 2008 may be used bythe modulator 2009 to provide a modulated RF carrier signal. Asdiscussed above, the RF carrier frequency can be referred to as thestimulus carrier frequency. The modulated RF carrier signal may beamplified by amplifier 2006 to generate the transmission signal. Adirectional coupler 2109 may be utilized to provide two-way coupling sothat both the forward power of the transmission signal flow transmittedby the TX antenna 2108 and the reverse power of the reflectedtransmission may be picked up by power detector 2122 of telemetryfeedback module 2102. In some implementations, a separate communicationantenna 2106 may function as the receive antenna for receiving telemetryfeedback signal from implantable, passive stimulation device 2022. Insome configurations, the communication antenna may operate at a higherfrequency band than the TX antenna 2108. For example, the communicationantenna 2106 may have a characteristic frequency that is a secondharmonic of the characteristic frequency of TX antenna 2108, asdiscussed above.

In some embodiments, the microwave field stimulator 2002 mayadditionally include a telemetry feedback module 2102. In someimplementations, the telemetry feedback module 2102 may be coupleddirectly to communication antenna 2106 to receive telemetry feedbacksignals. The power detector 2122 may provide a reading of both theforward power of the transmission signal and a reverse power of aportion of the transmission signal that is reflected duringtransmission. The telemetry signal, forward power reading, and reversepower reading may be amplified by low noise amplifier (LNA) 2124 forfurther processing. For example, the telemetry module 2102 may beconfigured to process the telemetry feedback signal by demodulating thetelemetry feedback signal to extract the encoded information. Suchencoded information may include, for example, a status of implantable,passive stimulation device 2022 and one or more electrical parametersassociated with a particular channel (electrode) of the implantable,passive stimulation device 2022. Based on the decoded information, thetelemetry feedback module 2102 may be used to calculate an operationalcharacteristic of implantable, passive stimulation device 2022.

Some embodiments of the MFS 2002 may further include a power managementmodule 2104. A power management module 2104 may manage various powersources for the MFS 2002. Example power sources include, but are notlimited to, lithium-ion or lithium polymer batteries. The powermanagement module 2104 may provide several operational modes to savebattery power. Example operation modes may include, but are not limitedto, a regular mode, a low power mode, a sleep mode, a deepsleep/hibernate mode, and an off mode. The regular mode providesregulation of the transmission of transmission signals and stimulus tothe implantable passive stimulation device 2022. In this regular mode,the telemetry feedback signal is received and processed to monitor thestimuli as normal. Low-power mode also provides regulation of thetransmission of transmission signals and stimulus to the electrodes ofthe implantable, passive stimulation device 2022. However, under thismode, the telemetry feedback signal may be ignored. More specifically,the telemetry feedback signal encoding the stimulus power may beignored, thereby saving MFS 2002 overall power consumption. Under sleepmode, the transceiver and amplifier 2006 are turned off, while themicrocontroller is kept on with the last saved state in its memory.Under the deep sleep/hibernate mode, the transceiver and amplifier 2006are turned off, while the microcontroller is in power down mode, butpower regulators are on. Under the off mode, all transceiver,microcontroller and regulators are turned off achieving zero quiescentpower.

FIG. 22 is a flowchart showing an example process in which the MFS 2002transmits polarity setting information to the implantable, passivestimulation device 2022.

Polarity assignment information is stored in a non-volatile memory(2202) within the microcontroller 2008 of the MFS 2002. The polarityassignment information may be representative-specific and may be chosento meet the specific need of a particular patient. Based on the polarityassignment information chosen for a particular patient, themicrocontroller 2008 executes a specific routine for assigning polarityto each electrode of the electrode array of the implantable, passivestimulation device 2022. The particular patient has an implantable,passive stimulation device 2022 implanted, as described above.

In some implementations, the polarity assignment procedure includessending a signal to the implantable, passive stimulation device 2022with an initial power-on portion followed by a configuration portionthat encodes the polarity assignments. The power-on portion may, forexample, simply include the RF carrier signal (e.g., at the stimuluscarrier frequency). The initial power-on portion has a duration that issufficient to power-on the stimulator and allow the stimulator to resetinto a configuration mode. Once in the configuration mode, thestimulator reads the encoded information in the configuration portionand sets the polarity of the electrodes as indicated by the encodedinformation.

Thus, in some implementations, the microcontroller 2008 turns on themodulator 2009 so that the unmodulated RF carrier is sent to theimplantable, passive stimulation device 2022 (2204). After apre-determined duration, the microcontroller 2008 automaticallyinitiates transmitting information encoding the polarity assignment. Inthis scenario, the microcontroller 2008 transmits the polarity settingsin the absence of handshake signals from the implantable, passive neuralstimulator. Because the MFS 2002 is operating in close proximity toimplantable, passive stimulation device 2022, signal degradation may notbe severe enough to warrant the use of handshake signals to improvequality of communication.

To transmit the polarity information, the microcontroller 2008 reads thepolarity assignment information from the non-volatile memory andgenerates a digital signal encoding the polarity information (2206). Thedigital signal encoding the polarity information may be converted to ananalog signal, for example, by a digital-to-analog (DAC) converter(2212). The analog signal encoding the waveform may modulate a carriersignal at modulator 2009 to generate a configuration portion of thetransmission signal (2214). The frequency of this carrier signal is thestimulus carrier frequency. This configuration portion of thetransmission signal may be amplified by the power amplifier 2006 togenerate the signal to be transmitted by antenna 2007 (2216).Thereafter, the configuration portion of the transmission signal istransmitted to implantable, passive neural stimulation device 2022(2218).

Once the configuration portion is transmitted to the implantable,passive neural stimulation device 2022, the microcontroller 2008initiates the stimulation portion of the transmission signal. Similar tothe configuration portion, the microcontroller 2008 generates a digitalsignal that encodes the stimulation waveform. The digital signal isconverted to an analog signal using the DAC. The analog signal is thenused to modulate a carrier signal at modulator 2009 to generate astimulation portion of the transmission signal. The frequency of thiscarrier signal is also at the stimulus carrier frequency.

In other implementations, the microcontroller 2008 initiates thepolarity assignment protocol after the microcontroller 2008 hasrecognized a power-on reset signal transmitted by the implantable,passive stimulation device 2022. The power-on reset signal may beextracted from a feedback signal received by microcontroller 2008 fromthe implantable passive neural stimulator. The feedback signal may alsobe known as a handshake signal in that it alerts the MFS 2002 of theready status of the implantable, passive stimulation device 2022. In anexample, the feedback signal may be demodulated and sampled to digitaldomain before the power-on reset signal is extracted in the digitaldomain.

FIG. 23 is a flow chart showing an example of the process in which MFS2002 receives and processes the telemetry feedback signal to makeadjustments to subsequent transmissions.

In some implementations, the microcontroller 2008 polls the telemetryfeedback module 2102 (2312). The polling is to determine whether atelemetry feedback signal has been received (2314). The telemetryfeedback signal may include information based on which the MFS 2002 mayascertain the power consumption being utilized by the electrodes of theimplantable, passive stimulation device 2022. This information may alsobe used to determine the operational characteristics of the combinationsystem of the MFS 2002 and the neural stimulator 2022, as will bediscussed in further detail in association with FIG. 24. The informationmay also be logged by MFS 2002 so that the response of the patient maybe correlated with past treatments received over time. The correlationmay reveal the patient's individual response to the treatments thepatient has received up to date.

If the microcontroller 2008 determines that telemetry feedback module2102 has not yet received telemetry feedback signal, microcontroller2008 may continue polling (2312). If the microcontroller 2008 determinesthat telemetry feedback module 2102 has received telemetry feedbacksignal, the microcontroller 2008 may extract the information containedin the telemetry feedback signal to perform calculations (2316). Theextraction may be performed by demodulating the telemetry feedbacksignal and sampling the demodulated signal in the digital domain. Thecalculations may reveal operational characteristics of the implantable,passive stimulation device 2022, including, for example, voltage orcurrent levels associated with a particular electrode, power consumptionof a particular electrode, and/or impedance of the tissue beingstimulated through the electrodes.

Thereafter, in certain embodiments, the microcontroller 2008 may storeinformation extracted from the telemetry signals as well as thecalculation results (2318). The stored data may be provided to a userthrough the programmer upon request (2320). The user may be the patient,the doctor, or representatives from the manufacturer. The data may bestored in a non-volatile memory, such as, for example, NAND flash memoryor EEPROM.

In other embodiments, a power management schema may be triggered (2322)by the microcontroller 2008. Under the power management schema, themicrocontroller 2008 may determine whether to adjust a parameter ofsubsequent transmissions (2324). The parameter may be amplitude of thestimulation waveform or the stimulation waveform shape. In oneimplementation, the amplitude level may be adjusted based on a lookuptable showing a relationship between the amplitude level and acorresponding power applied to the tissue through the electrodes. In oneimplementation, the waveform shape may be pre-distorted to compensatefor a frequency response of the MFS 2002 and implantable, passivestimulation device 2022. The parameter may also be the carrier frequencyof the transmission signal (known as the stimulus carrier frequency).For example, this carrier frequency of the transmission signal may bemodified to provide fine-tuning that improves transmission efficiency.Detailed examples of parameter adjustment will be discussed inassociation with FIG. 25B.

If an adjustment is made, the subsequently transmitted transmissionsignals are adjusted accordingly. If no adjustment is made, themicrocontroller 2008 may proceed back to polling the telemetry feedbackmodule 2102 for telemetry feedback signal (2312).

In other implementations, instead of polling the telemetry feedbackmodule 2102, the microcontroller 2008 may wait for an interrupt requestfrom telemetry feedback module 2102. The interrupt may be a softwareinterrupt, for example, through an exception handler of the applicationprogram. The interrupt may also be a hardware interrupt, for example, ahardware event and handled by an exception handler of the underlyingoperating system.

FIG. 24 is a schematic of an example implementation of the power, signaland control flow for the implantable, passive stimulation device 2022. ADC source 2402 obtains energy from the transmission signal received atstimulation device 2022 during the initial power-on portion of thetransmission signal while the RF power is ramping up. In oneimplementation, a rectifier may rectify the received power-on portion togenerate the DC source 2402 and a capacitor 2404 may store a charge fromthe rectified signal during the initial portion. When the stored chargereaches a certain voltage (for example, one sufficient or close tosufficient to power operations of the implantable, passive stimulationdevice 2022), the power-on reset circuit 2406 may be triggered to send apower-on reset signal to reset components of the implantable, passivestimulation device 2022. The power-on set signal may be sent to circuit2408 to reset, for example, digital registers, digital switches, digitallogic, or other digital components, such as transmit and receive logic2410. The digital components may also be associated with a controlmodule 2412. For example, a control module 2412 may include electrodecontrol 252, register file 1532, etc. The power-on reset may reset thedigital logic so that the circuit 2408 begins operating from a known,initial state.

In some implementations, the power-on reset signal may subsequentlycause circuit 2408 to transmit a power-on reset telemetry signal back toMFS 2002 to indicate that the implantable, passive stimulation device2022 is ready to receive the configuration portion of the transmissionsignal that contains the polarity assignment information. For example,the control module 2412 may signal the RX/TX module 2410 to send thepower-on reset telemetry signal to the RF out antenna 2432 fortransmission to MFS 2002. Circuit 2408 may be an FGPA circuit.

In other implementations, the power-on reset feedback signal may not beprovided. As discussed above, due to the proximity between MFS 2002 andimplantable, passive stimulator device 2022, signal degradation due topropagation loss may not be severe enough to warrant implementations ofhandshake signals from the implantable, passive stimulation device 2022in response to the transmission signal. In addition, the operationalefficiency of implantable, passive stimulation device 2022 may beanother factor that weighs against implementing handshake signals.

Once the circuit 2408 has been reset to an initial state, the circuit2408 transitions to a configuration mode configured to read polarityassignments encoded on the received transmission signal during theconfiguration portion. In some implementations, the configurationportion of the transmission signal may arrive at implantable, passivestimulation device through RF in antenna 2434. The transmission signalreceived may provide an AC source 2414. The AC source 2414 may be at thecarrier frequency of the transmission signal, for example, from about300 MHz to about 8 GHz.

Thereafter, the control module 2412 may read the polarity assignmentinformation and set the polarity for each electrode through the analogmux control 2416 according to the polarity assignment information in theconfiguration portion of the received transmission signal. The electrodeinterface 252 may be one example of analog mux control 2416, which mayprovide a channel to a respective electrode of the implantable, passivestimulation device 2022.

Once the polarity for each electrode is set through the analog muxcontrol 2416, the implantable, passive stimulation device 2022 is readyto receive the stimulation waveforms. Some implementations may notemploy a handshake signal to indicate the stimulation device 2022 isready to receive the stimulation waveforms. Rather, the transmissionsignal may automatically transition from the configuration portion tothe stimulation portion. In other implementations, the implantable,passive stimulation device 2022 may provide a handshake signal to informthe MFS 2002 that implantable, passive stimulation device 2022 is readyto receive the stimulation portion of the transmission signal. Thehandshake signal, if implemented, may be provided by RX/TX module 2410and transmitted by RF out antenna 2432.

In some implementations, the stimulation portion of the transmissionsignal may also arrive at implantable, passive stimulation devicethrough RF in antenna 2434. The transmission signal received may providean AC source 2414. The AC source 2414 may be at the carrier frequency ofthe transmission signal, for example, from about 300 MHz to about 8 GHz.The stimulation portion may be rectified and conditioned in accordancewith discussions above to provide an extracted stimulation waveform. Theextracted stimulation waveform may be applied to each electrode of theimplantable, passive stimulator device 2022. In some embodiments, theapplication of the stimulation waveform may be concurrent, i.e., appliedto the electrodes all at once. As discussed above, the polarity of eachelectrode has already been set and the stimulation waveform has beenapplied to the electrodes in accordance with the polarity settings.

In some implementations, each channel of analog mux control 2416 isconnected to a corresponding electrode and may have a reference resistorplaced serially. For example, FIG. 24 shows reference resistors 2422,2424, 2426, and 2428 in a serial connection with a matching channel.Analog mux control 2416 may additionally include a calibration resistor2420 placed in a separate and grounded channel. The calibration resistor2420 is in parallel connection with a given electrode on a particularchannel. The reference resistors 2422, 2424, 2426, and 2428 as well asthe calibration resistor 2420 may also be known as sensing resistors1518. These resistors may sense an electrical parameter in a givenchannel, as discussed below.

In some configurations, an analog controlled carrier modulator mayreceive a differential voltage that determines the carrier frequencygenerated. This carrier frequency may be referred to as the feedbackcarrier frequency, which may be distinct from the stimulus carrierfrequency associated with the transmission signal discussed earlier. Thegenerated carrier frequency may be proportional to the differentialvoltage. An example analog controlled carrier modulator is VCO 1533, asdiscussed above in association with FIG. 15.

In one configuration, the carrier frequency may indicate an absolutevoltage, measured in terms of the relative difference from apre-determined and known voltage. For example, the differential voltagemay be the difference between a voltage across a reference resistorconnected to a channel under measurement and a standard voltage. Thedifferential voltage may be the difference between a voltage acrosscalibration resistor 2420 and the standard voltage. One example standardvoltage may be the ground.

In another configuration, the feedback carrier frequency may reveal animpedance characteristic of a given channel. For example, thedifferential voltage may be the difference between the voltage over theelectrode connected to the channel under measurement and a voltageacross the reference resistor in serial connection. Because of theserial connection, a comparison of the voltage across the referenceresistor and the voltage over the electrode would indicate the impedanceof the electrode and the underlying tissue being stimulated relative tothe impedance of the reference resistor. As the reference resistor'simpedance is known, the impedance of the electrode and the underlyingtissue being stimulated may be inferred based on the resulting feedbackcarrier frequency. Because the electrodes may only provide aninsignificant contact impedance, the impedance of the electrode and theunderlying tissue being stimulated may be dominated by the impedance ofthe underlying tissue being stimulated.

For example, the differential voltage may be the difference between avoltage over the calibration resistor and a voltage across the referenceresistor. Because the calibration resistor is placed in parallel to agiven channel, the voltage over the calibration is substantially thesame as the voltage over the given channel. Because the referenceresistor is in a serial connection with the given channel, the voltageover the reference resistor is a part of the voltage across the givenchannel. Thus, the difference between the voltage over the calibrationresistor and the voltage across the reference resistor correspond to thevoltage drop over the electrode. Hence, the voltage over the electrodemay be inferred based on the voltage difference.

In yet another configuration, the feedback carrier frequency may providea reading of a current. For example, if the voltage over referenceresistor 2422 has been measured, as discussed above, the current goingthrough reference resistor and the corresponding channel may be inferredby dividing the measured voltage by the impedance of reference resistor2422.

Many variations may exist in accordance with the specifically disclosedexamples above. The examples and their variations may sense one or moreelectrical parameters concurrently and may use the concurrently sensedelectrical parameters to drive an analog controlled modulator device.The resulting carrier frequency varies with the differential of theconcurrent measurements. This carrier frequency may be referred to asthe feedback carrier frequency for transmitting the telemetry feedbacksignal to MFS 2002. The telemetry feedback signal may include a signalat the resulting feedback carrier frequency.

The MFS 2002 may determine the feedback carrier frequency variation bydemodulating at a fixed frequency and measure phase shift accumulationcaused by the feedback carrier frequency variation. Generally, a fewcycles of RF waves at the resulting feedback carrier frequency may besufficient to resolve the underlying feedback carrier frequencyvariation. The determined variation may indicate an operationcharacteristic of the implantable, passive stimulation device 2022. Theoperation characteristics may include an impedance, a power, a voltage,a current, etc. The operation characteristics may be associated with anindividual channel. Therefore, the sensing and feedback carrierfrequency modulation may be channel specific and applied to one channelat a given time. Consequently, the telemetry feedback signal may be timeshared by the various channels of the implantable, passive stimulationdevice 2022.

In one configuration, the analog MUX 2418 may be used by the controllermodule 2412 to select a particular channel in a time-sharing scheme. Thesensed information for the particular channel, for example, in the formof a carrier frequency modulation, may be routed to RX/TX module 2410.Thereafter, RX/TX module 2410 transmits, through RF out antenna 2432, tothe MFS 2002, the telemetry feedback encoding the sensed information forthe particular channel.

FIG. 25A shows an example RF carrier wave and example envelope waveformssuitable for use as stimulation waveforms. The frequency of this RFcarrier wave may be known as the stimulus carrier frequency, asdiscussed earlier. The top panel shows an example waveform correspondingto the RF carrier. As discussed above, the RF carrier may be in amicrowave band with a center frequency from about 300 MHz to about 8GHz. The remaining panels show example envelope waveforms suitable to beused as stimulation waveforms. Examples include, but are not limited to,a square wave, a Gaussian waveform, a decaying exponential waveform, aroot raised cosine waveform. The envelope waveform may modulate the RFcarrier (at the stimulus carrier frequency) to generate to generate anoutput signal to feed the power amplifier 2006. This modulated andamplified signal correspond to a stimulation portion of a transmissionsignal. The implantable, passive neural stimulator may decoded thereceived transmission signal to extract the stimulation waveform byrectifying the transmission signal and conditioning the rectifiedsignal, as discussed above.

FIG. 25B shows an example of pre-distorted stimulation waveform tooffset distortions caused by the MFS 2002 and the implantable, passivestimulation device 2022 as well as the impedance characteristic of thetissue being stimulated. The top panel shows an example of anun-equalized transmission signal modulated by a square waveform. Toreach the electrodes, the transmission signal generally undergoes thetransmission from the antenna 2007 on MFS 2002, the propagation throughskin and underlying tissue, the reception by the RX antenna 2023 of theimplantable, passive stimulation device 2022, and the application at theelectrodes with a frequency response. The combined effect amounts to aband pass characteristic in the frequency domain. A resulting actualstimulus applied may deviate substantially from the intended waveformshape, as shown in the top panel of FIG. 25B.

To compensate for this band pass effect, the stimulation waveform may bepre-distorted. The pre-distortion may be based on the inverse frequencyresponse of the band pass effect. By imposing the inverse frequencyresponse to provide a pre-distorted waveform shape, the receivedstimulation waveform at the implantable, passive stimulation device 2022may match the desired waveform shape. The bottom panel of FIG. 25B showsa pre-equalized transmission signal modulated by a pre-distorted squarewaveform. As illustrated, the pre-equalized transmission signal canoffset the band pass effect so that the actual stimulus applied maysubstantially match the intended square waveform shape.

In some implementations, the pre-equalization may be applied based oninformation in the telemetry feedback signal from the implantable,passive stimulation device 2022. In other implementations, the amplitudeor frequency of the transmission signal may be adjusted based on theinformation in the telemetry signal, as discussed above in associationwith FIG. 23.

In one configuration, the amplitude may be adjusted according to datastored in a table on the MFS 2002. The table may, for example, provide achart showing, for a desired power output at the electrodes, thecorresponding amplitude of the transmission signal. The amplitude of thetransmission may be increased if the calculated power is below thedesired power in accordance with the chart. Likewise, the amplitude ofthe transmission may be reduced if the calculated power is above thedesired power.

In another configuration, the stimulus carrier frequency may be adjustedso that the transmission signal may be better tuned to the combined bandpass effect as discussed above. The adjustment may be in the megahertzrange, for example, up to 10 MHz, to provide fine tuning to the carrierfrequency. The fine tuning may improve the efficiency of transmittingthe stimulation portion of the transmission signal from MFS 2002 toimplantable, passive stimulation device 2022. In certain situations,patient body movement during a treatment session may necessitate suchfine tuning to maintain substantially identical stimulus over thetreatment session.

FIG. 26

is a timing diagram showing example waveforms during the initial portionand the subsequent configuration portion of a transmission signalreceived at the implantable, passive stimulation device 2022. The toppanel 2602 shows an example waveform corresponding to the RF carriertransmitted by the MFS 2002. As discussed above, the RF carrier may bein a microwave band with a center frequency from about 300 MHz to about8 GHz.

Panel 2604 shows the power supply received at implantable, passiveneural stimulation device 2022. The initial portion corresponds to apower ramp-up. When implantable, passive neural stimulation device 2022has received enough power for operation, a power-on event signal may begenerated by a power-on reset circuit 2406. The power-on reset signal,shown in panel 2606, may be used to reset the component son thestimulation device 2022 as described above.

Thereafter, the stimulation device 2022 is ready to receive theconfiguration portion. Panel 2608 shows example waveforms received byimplantable, passive stimulation device 2022 during the configurationportion. The configuration portion may include N data cycles to encodethe polarity assignment information for each channel of the implantable,passive neural stimulation device 2022. In some implementations, for aparticular channel, the configuration portion may contain several datacycles to encode the channel identification information. Theconfiguration portion may contain additional data cycles to encode thepolarity assignment of the particular channel. In some implementations,the waveform edges may be used to encode the channel identificationinformation and the corresponding polarity assignment information forthe channel. For example, the rising edge may denote a “1” while thefalling edge may denote a “0.” Edge triggered encoding may be morerobust than static level encoding for transmitting the polarityassignment information. The channel identification information and thecorresponding polarity assignment information may then be stored, forexample, in register file 1532. Controller module 2412 may set thepolarity of a particular channel according to the information stored inthe register file 1532, as discussed above and indicated by panel 2610.

Thus, the polarity assignment information of each channel may bemaintained persistent at the implantable passive stimulation device 2022by providing the information during the configuration portion of atransmission signal before a stimulation is subsequently appliedaccording to the assigned polarity.

FIG. 27 is a timing diagram showing example waveforms during the finalstimulation portion of the transmission signal received at theimplantable, passive stimulation device 2022. As discussed above, atransmission signal may include an initial portion containing energy topower up the implantable, passive stimulation device 2022, a subsequentconfiguration portion containing polarity assignment information forimplantable, passive stimulation device 2022 to set the polarities ofthe electrodes. Panel 2712 illustrates the RF carrier modulated by thestimulation waveform, as synthesized by microcontroller 2008 andmodulator 2009 and then amplified by amplifier 2006. The stimulationportion of the received transmission signal may be rectified andconditioned to provide the received stimulation waveform, as shown inpanel 2714. The envelope detection is performed at the implantablepassive stimulation device 2022, as discussed above. At the end of eachstimulation waveform, a telemetry feedback signal may be provided by theimplantable, passive stimulation device 2022 in accordance withdiscussions above. The timing of when the telemetry signal is providedand transmitted to MFS 2002 is illustrated in panel 2716. As discussedabove, the telemetry signal may provide information of an operationcharacteristic of one channel at a given time instant. For example,panel 2716 shows channels 1 through 3 are being measured individuallyand the corresponding telemetry feedback signal is provided on atime-sharing basis.

FIG. 28 is a block diagram illustrating an example in which a userprograms the stimulation waveform to be embedded in the signal sequencefor transmission to the implantable, passive stimulation device 2022.The programmer 2012 may be a mobile computing device. The programmer2012 may communicate with the MFS 2002 via, for example, blue-tooth orUSB. The user may authenticate him or herself to the MFS before he canaccess data on the MFS 2002 or modify existing settings on the MFS 2002.The communication may also be encrypted.

A user may modify a setting of the MFS 2002 by, for example, choosing apreset program or using a button control (2804). A user of theprogrammer 2012 may be presented with a user interface (UI) 2800. The UI2800 may be a visual programming interface to provide easy access toprogramming capabilities. The UI 2800 may provide a collection of presetprograms that the user may choose to apply to his treatment. The presetprograms A, B, and C may be provided by the manufacturer as treatmentprotocols in compliance with any regulatory provisions. The presetprograms may prescribed by an attending physician as the treatment plansmost likely to be efficacious for the user/patient. The UI 2008 may alsoprovide a button for the user/patient to adjust a power level of thestimuli to be or being applied.

In some implementations, the UI 2800 may provide debouncing in responseto user inputs. After receiving user selections as made on the UI 2008,waveform parameters stored in a non-volatile memory may be activated(2802) so that the micro-controller 2008 may synthesize an output signalbased on the waveform parameters. The synthesized output signal may beconverted into an analog signal (2806). As discussed above, the analogsignal may modulate a carrier frequency to provide a modulated signal(2216), the modulated signal may be subsequently amplified by amplifier2006 (2216), and the amplified signal may be transmitted from the MFS2002 to the implantable, passive stimulation device 2022 (2218).

FIG. 29A shows an example UI 2800 for the user to program thestimulation waveform. The UI 2800 may include a name label 2902indicating the name of the patient registered to MFS 2002, a batteryindicator 2904, a menu of preset programs 2906 for the user to choosefrom, bar indicators 2908 to indicate the amplitude or power of thestimuli, program button 2910 for the user to scroll through the menu ofpreset programs 2906, and an amplitude button 2912 for the user toadjust the amplitude or power of the stimuli. The UI 2800 mayadditionally include an advanced button for the user to access advancedor more sophisticated options of programming MFS 2002, a simple buttonfor the user to access standard options of programming MFS 2002, an asettings button for the user to change settings on MFS 2002. The UI 2800of FIG. 29A corresponds to a UI under the advanced option. The UI 2800may further include power button 2920 to power on or off MFS 2002.

FIG. 29B shows another example UI 2800 for the user to program thestimulation waveform. UI 2800 of FIG. 29B correspond to the UI after thesimple option is selected. The UI 2800 may include an interactivequestionnaire 2922 for the user to supply information of the user'scurrent feeling and past treatment history. Questionnaire 2922 mayinclude icon bar 2924 to guide the user to convey the user's need formore (2926) or less (2928) stimulation. Questionnaire 2922 may alsoinclude button 2930 and button 2932 to convey the user's desire tochange to a different preset program. Questionnaire may additionallyinclude an indicator 2934 to notify the user of battery power status.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A system for modulating excitable tissue in apatient comprising: an implantable passive neural stimulation devicecomprising one or more electrodes and an embedded dipole receivingantenna; and a controller module comprising: a storage device configuredto store parameters defining a stimulation waveform and polarityassignments for the electrodes; a controller configured to generate,based on the parameters, an output signal that includes the stimulationwaveform and RF energy for operation of the implantable passive neuralstimulation device, wherein the output signal additionally includes thepolarity assignments for the electrodes in the implantable passiveneural stimulation device; a modulator configured to modulate a carriersignal with the output signal to generate a transmission signal, whereinthe carrier signal has a frequency between about 800 MHz to 6 GHz; andone or more antennas configured to transmit the transmission signal tothe implantable passive neural stimulation device such that theimplantable passive neural stimulation device uses energy solely fromthe transmission signal for operation without the need for long termenergy storage in the implantable passive neural stimulation device,sets the polarities for the electrodes in the implantable passive neuralstimulation device based on the polarity assignments, generateselectrical pulses using the RF energy from the transmission signal, andapplies the electrical pulses to the excitable tissue, when theimplantable passive neural stimulation device is placed at a target site1 cm to 6 cm below an outer skin surface of the patient and when thecontroller module is placed at a location exterior to the patient andspaced away from the outer skin of the patient.
 2. The system of claim 1wherein: the stimulation waveform includes a sequence of pulses and theparameters include at least one of: a pulse duration, pulse amplitude,and a pulse repetition rate; and the output signal generated by thecontroller includes a configuration portion that encodes the polarityassignments and a stimulation portion that includes the stimulationwaveform.
 3. The system of claim 2, wherein the controller module isconfigured to: generate the transmission signal such that thetransmission signal has an initial power-on portion that precedes theconfiguration portion and the stimulation portion, the initial power-onportion being sent to the implantable passive neural stimulation deviceas part of the transmission signal such that the implantable passiveneural stimulation device stores energy from the initial power-onportion and sends a power-on event signal when the energy reaches athreshold amount.
 4. The system of claim 3, wherein the controllermodule is further configured to: receive the power-on event signal fromthe implantable passive neural stimulation device; in response toreceiving the power-on event signal, generate the configuration portionthat is sent to the implantable passive neural stimulation device; andafter generating the configuration portion, generate the stimulationportion.
 5. The system of claim 2, wherein the configuration portionincludes multiple waveforms that encode the polarity assignments.
 6. Thecontroller module of claim 1 further comprising a rechargeable powersource configured to be managed by a power management protocol.
 7. Thesystem of claim 6, wherein the rechargeable power source includes oneof: a lithium-ion battery, a lithium polymer battery.
 8. The system ofclaim 1, further comprising a programmer module having a visualprogramming interface to enable a user to program the controller module.9. The system of claim 8, wherein the visual programming module isconfigured to authenticate the user and thereafter provide accesscontrol to the user.
 10. The system of claim 1, wherein: the one or moreantennas are further configured to receive telemetry feedback signalsfrom the implantable passive stimulation device in response to thetransmission signal, and the controller is further configured to modifythe output signal by using a closed-loop feedback control based on thereceived telemetry feedback signal.
 11. The system of claim 10, whereinthe controller is further programmed to apply the closed-loop feedbackcontrol by: ascertaining a distortion to the electrical pulses asapplied by the electrodes of the implantable, passive neural stimulationdevice, the distortion caused by at least one of a transmissioncharacteristic of the antenna, a characteristic of the implantablepassive neural stimulator, or an impedance characteristic of the tissue;and adjusting the stimulation waveform embedded in the transmissionsignal to compensate for the distortion such that the electrical pulsesas applied are substantially undistorted despite the transmissioncharacteristic of the antenna, the characteristic of the implantablepassive neural stimulator, or the impedance characteristic of thetissue.
 12. The system of claim 11, wherein the distortion ischaracterized as a frequency response corresponding to at least one ofthe transmission characteristic of the antenna, the characteristic ofthe implantable passive neural stimulator, and the impedancecharacteristic of the tissue.
 13. The system of claim 12, wherein thecontroller is configured to adjust the stimulation waveform by filteringthe transmission signal according to an inverse of the frequencyresponse, performing linear pre-equalization for the transmit signal.14. The system of claim 10, wherein the controller is further programmedto apply the closed-loop feedback control by: monitoring a stimulusamplitude being directed to the excitable tissue through the electrodesbased on information contained in the telemetry feedback signal; andadjusting a parameter associated with the stimulation waveform embeddedin the transmission signal such that the stimulus amplitude remainssubstantially constant.
 15. The system of claim 14, wherein thecontroller is further configured to change the stimulus amplitude basedon patient body movement.
 16. The system of claim 14, wherein theparameter is an amplitude level associated with the stimulation waveformembedded in the transmission signal, and the amplitude level is adjustedbased on known relationship between the amplitude level and acorresponding stimulus amplitude applied to the tissue through theelectrodes.
 17. The system of claim 14 wherein the controller is furtherconfigured to adjust the parameter by modifying the carrier frequencywithin a range of up to 10megahertz.
 18. The system of claim 1, whereinthe storage device comprises non-volatile memory including at least oneof: an EEPROM, a flash memory.
 19. The system of claim 1, wherein thecontroller module is configured for placement exterior to the patientwithin a 3-feet radius of the implantable passive neural stimulationdevice.
 20. The system of claim 1, wherein the controller module isconfigured for a sub-cutaneous implantation in a patient.